I think the author doesn't realize how much money prop trading firms make off you even if you "just invest in the S&P 500". Between changes in index makeup, dif

I think the author doesn't realize how much money prop trading firms make off you even if you "just invest in the S&P 500". Between changes in index makeup, differences between underlying and derived instruments, and the need for the ETF to keep the required balance of actuals, there's quite a bit of movement to make money off of. And it's not exactly hidden knowledge when which large pension/mutual funds make their adjustments.