[reducesuffering]

Isn't it actually neither buy nor sell? Most common indices (by AUM) are market-cap weighted. If a total market ETF contains 0.25% of it in GME, and GME doubles in value, it's GME it holds is now 0.50%, and that's how much it should hold now, according to market-cap weight. No buying or selling.

Of course there's many ETF's that aren't market-cap weighted, but the majority of funds/value is.

[boatsie]

That’s right, I misspoke. It could possibly require other funds that were tracking, say, the top 1000 stocks by market cap to buy, not ones tracking the regular index.