OR, since index funds are constantly getting 401(k) money dumped into them and therefore establish a reputation for a type of asset that has guaranteed returns

OR, since index funds are constantly getting 401(k) money dumped into them and therefore establish a reputation for a type of asset that has guaranteed returns with no risk, will develop into a massive asset bubble that will eventually go kablammo and take the retirement savings of half of the world down with them. You have way too much faith in people making well informed decisions.