The more investors index, the higher the costs for those that don’t, according to a recent MarketWatch article.

The benefit of indexing–lower costs and higher long-term returns—only exists, the article argues, if there is an “active, functioning market underlying whatever index a fund is trying to capture the performance of.” The problem arises, it asserts, in that the market can’t exist without active investments born of research and analysis that serve to set prices on individual issues. The vicious cycle comes as the low-cost nature of index investing attracts more investors, which leads to higher costs for non-indexers, which only attracts more dollars to indexing.

It quotes index fund trailblazer John Bogle who commented at this year’s Berkshire Hathaway annual meeting, “If everybody indexed, the only word you could use is chaos, catastrophe.” The Vanguard founder stressed, however, that there is long way to go before such an event would happen. Morningstar data shows that, as of April, 46.7% of assets invested in U.S. equities through index funds, up from 36.3% three years prior.

According to the article, if the market were to experience a prolonged downturn, active managers could “gain an edge over indexers by moving large portions of assets into cash or into defensive sectors such as utilities and consumer staples.” Until then, it says, indexing will probably continue to grow. For now, it says, while indexing is a good choice for many investors, they should “remember that many sensible ideas, especially in investing, make less sense as more people put them into practice.”