The Structural Risks of Passive Investing: Price Discovery and Common Ownership

The Same Three Names, Over and Over

Pull up the shareholder list of almost any large American company — a bank, an airline, a chipmaker, two companies that directly compete with each other — and near the top you'll almost always find the same three names: BlackRock, Vanguard, and State Street. These firms didn't individually decide these companies were worth owning. They're simply the managers of the ETFs and index funds that millions of ordinary investors put money into, and those funds mechanically buy whatever sits in the index they track. This lesson covers two structural debates that come out of passive money now representing such a large share of the market: whether it's weakening the market's ability to set accurate prices, and whether it's concentrating voting power over corporate America into a small number of hands. Both are live, unsettled arguments among economists and regulators — not conclusions this lesson is trying to hand you.

How Passive Money Got This Big

As covered in ETF Basics, a fund that simply replicates an index lets an investor capture the market's return at a fraction of the cost of picking stocks, and that value proposition has driven explosive growth in index investing over the past few decades. As discussed in Efficient Market Hypothesis vs. Behavioral Finance, the more evidence accumulated that active managers struggle to consistently beat the market after fees, the more investors concluded that simply buying the index was the rational choice. The result: by the mid-2020s, BlackRock, Vanguard, and State Street together managed well over $20 trillion in combined assets, and several academic estimates put their combined stake above 20% of a large number of S&P 500 companies. The catch is that this money didn't arrive because anyone judged the company's earnings or outlook — it arrived, and leaves, mechanically, purely because the company sits inside an index.

The First Debate: Is Price Discovery Breaking Down?

For markets to do their job, good companies are supposed to see their stock rise and bad companies are supposed to see theirs fall. Economists call this process price discovery, and historically it's been driven by active investors analyzing fundamentals — buying what looks cheap, selling what looks expensive. Passive money does the opposite. As covered in The Index Rebalancing Effect, index funds and ETFs buy and sell based purely on a stock's weight in an index, with no view on the company at all. That's harmless while passive money is a small slice of the market. The concern is that once it becomes a large enough slice, a self-reinforcing loop can emerge: a stock that already carries a heavier index weight pulls in more mechanical buying regardless of price, which can push its weight even higher. Michael Burry, famous for calling the 2008 housing bubble, compared this dynamic in a 2019 Bloomberg interview to the pre-2008 rush into subprime-backed CDOs, arguing that passive inflows were distorting individual stock and bond prices independent of fundamentals. That comparison is Burry's own framing, not a settled fact — the empirical research on how much passive growth has actually degraded price discovery is genuinely mixed. Some studies find index-member stocks trade with looser ties to their own fundamentals; others argue enough active capital remains in the market that any such effect is hard to detect reliably. The honest summary is that this is an open question without a clean answer, not a verdict either side has won.

The Second Debate: Common Ownership and Concentrated Voting Power

A second structural feature of passive money's growth is common ownership — the same handful of managers holding large stakes in companies that directly compete with each other. A widely cited 2017 study by Fichtner, Heemskerk, and Garcia-Bernardo found that BlackRock, Vanguard, and State Street were, individually or jointly, the single largest shareholder in roughly 88% of S&P 500 companies — a figure from 2017 that has plausibly grown given how much the three firms' combined assets have expanded since. Why this matters splits into two threads. The first is an antitrust concern: if the same asset manager holds large stakes in two competing airlines or banks, that manager's financial interest may lean toward both companies staying profitable together rather than competing aggressively on price — benefiting the manager's overall portfolio even if it means weaker competition for customers. The U.S. Federal Trade Commission has in fact started scrutinizing merger reviews more closely for common ownership among the parties' largest shareholders, and EU regulators have referenced common ownership in at least one merger decision. The second thread is a corporate-governance concern: when three asset managers' stewardship teams effectively decide how tens of thousands of shareholder votes get cast across nearly the entire market, voting power over real-world corporate decisions ends up concentrated in a strikingly small number of hands. The counterargument is substantial too — the Big Three vote with management on the overwhelming majority of proposals, and their individual stakes in any single company are usually well under 10%, which limits how much real leverage critics' narratives assume they have. BlackRock has also rolled out programs letting some clients vote their own shares directly, a response to exactly this kind of criticism.

The most frequently cited empirical test of the common-ownership-and-competition theory comes from the U.S. airline industry. Economists led by José Azar published research finding that routes where competing airlines shared heavy common ownership through the same asset managers tended to have relatively higher ticket prices. That paper is often treated as the strongest evidence for the theory, but other economists have pushed back hard on its methodology, arguing the effect doesn't reproduce reliably using the same underlying data. In other words, one study isn't enough to settle whether common ownership actually raises prices — it's still an active and genuinely contested area of economic research.

A Third Effect: Index Members Moving Together

As covered in Correlation and Diversification, diversification only works to the extent that the stocks you hold move somewhat independently of each other. Passive money complicates that, because it doesn't buy or sell based on which stock is the better business — it buys and sells based on which stocks share the same index membership. Several studies have found that stocks tend to become more correlated with each other simply by virtue of joining the same index, as they get bought and sold together by the same flows regardless of their individual fundamentals. The practical implication is that holding a dozen different index-member names may deliver less real diversification than it appears to on paper, since a meaningful share of their day-to-day co-movement is coming from shared fund flows rather than shared business risk.

Why This Matters Outside the U.S. Too

This debate centers on U.S. markets, but it isn't disconnected from investing anywhere else. As covered in How Exchange Rates Affect Foreign Investor Flows, a large share of the foreign money moving in and out of markets like Korea's tracks global benchmarks such as MSCI or FTSE, and that money moves mechanically with changes to a country's or stock's weight in those indexes — not with any judgment about the specific company. Domestic pension funds running large, rules-based rebalancing programs, as covered in NPS Strategic Asset Allocation and Rebalancing, create a similar category of fundamentals-blind, large-scale flow. The framework in this lesson — distinguishing flow-driven price moves from genuine changes in a company's value — applies just as directly to understanding foreign and institutional flows in any market, not only to U.S. mega-cap stocks.

What an Investor Should Actually Do With This

None of this amounts to "stop investing passively." The core advantage of passive investing — broad, diversified market exposure at very low cost — holds regardless of how these debates eventually get resolved, and the evidence on both price discovery and common ownership remains genuinely unsettled. What understanding this structure does change is sharper interpretation. First, news that a stock "joined an index" or "attracted passive inflows" tells you nothing about whether the underlying business improved — recognizing that distinction keeps you from mistaking mechanical flow for a fundamental signal. Second, as markets increasingly move in response to a small number of benchmark construction decisions made by a handful of large managers, it becomes worth asking whether a given stretch of returns reflects the specific company you picked or simply the index it happens to belong to. This isn't a tool for timing trades — it's background knowledge for understanding why markets sometimes behave differently than the simple story of buyers judging individual businesses would predict.

Takeaway

• BlackRock, Vanguard, and State Street together manage over $20 trillion through passive funds and ETFs, and sit as common top shareholders across most S&P 500 companies — a structure known as common ownership.
• The first debate is price discovery: passive money trades mechanically on index weight, not fundamentals, and Michael Burry compared this to the pre-2008 CDO bubble — but the empirical evidence on whether it has actually weakened price discovery is mixed, not settled.
• The second debate is common ownership and voting concentration: critics point to reduced competitive incentives and governance power concentrated in a few firms, while defenders point to the Big Three's management-friendly voting record and typically sub-10% individual stakes as reasons the real influence is more limited than it looks.
• A third, less-discussed effect is that stocks sharing an index tend to become more correlated with each other through shared fund flows, which can quietly erode the diversification benefit investors assume they're getting.
• The same dynamic shapes foreign passive flows into non-U.S. markets like Korea's and large rules-based rebalancers like national pension funds — it's a framework for reading flow-driven price moves, not a trading signal.

FAQ

Does this mean passive investing is dangerous?

No. These debates are about what happens to market structure as passive money's overall share grows — not about the product itself being unsafe for the individual investor who buys it. The low-cost, diversified-return advantage of indexing holds independent of how these structural questions eventually get resolved.

Do BlackRock and Vanguard actually control the companies they own?

They rarely vote against management in public shareholder meetings, which limits the case that they exert direct control. Some researchers argue real influence instead comes through private engagement with executives — sometimes called "hidden power" in the academic literature — but how large that influence actually is remains disputed between researchers and the asset managers themselves.

Can an individual investor avoid this by picking active funds or individual stocks instead?

Not entirely — the market as a whole is already shaped by how much money tracks major indexes, regardless of what any one investor personally holds. The point of this lesson isn't to offer an escape route; it's to help you read index-related news and flow data without mistaking it for a change in a company's actual value.

⚠️ This article is for informational purposes only and is not investment advice. The figures and research findings cited reflect estimates as of their original publication date; current figures should be confirmed against asset managers' own disclosures and more recent research. You are solely responsible for your own investment decisions.