In a Twitter thread, Elon Musk and Cathie Wood weighed in on the debate over the growing power of index funds, reports Bloomberg. Responding to a tweet from venture capitalist Marc Andreessen that said firms such as BlackRock Inc. have too much power because of the voting block created by their enormous passive vehicles, both Musk and Wood replied with criticism of passive investing.

While Musk, the CEO of Tesla Inc., said that passive investing has “gone too far,” Wood, the founder of Ark Investment Management, replied that the shift towards passive funds over the last 2 decades will eventually be seen as “a massive misallocation of capital.” She noted the number of investors in the S&P 500 who lost out on the big gains Tesla made before it joined the index.

But while Wood is one of the most well-known active managers on Wall Street, her firm’s flagship ARK Innovation ETF has been battered this year, declining nearly 45%, according to Bloomberg. For its part, Tesla is weighted into many benchmarks so that the company’s second- and third-largest shareholders are the indexing pioneers Vanguard Group and BlackRock, after Musk himself.

As passive funds snatch market shares from their active counterparts, the controversy over indexing and its risks has been growing. But the argument is nuanced and complicated, the article contends. Active managers use easily-traded, liquid passive funds within their own active strategies, as well as issue ETFs of their own in order to offer lower costs and more access. And many of their strategies make the fine line between indexing and stock picking very murky.

Passive strategies, meanwhile, have long had a very human hand working behind the curtain, from dictating the rules of each index to determining how every fund will be run. In fact, a 2021 study from Cornell University & the University of Technology Sydney found that in the U.S. equity market, the general activeness of investment hasn’t changed much at all for the past 20 years, the article concludes.