An index fund is a group of stocks. You buy them all together. That means that you're buying everything regardless if everything is worth buying. If tons of mon

An index fund is a group of stocks. You buy them all together. That means that you're buying everything regardless if everything is worth buying. If tons of money gets put into the index funds, all the prices rise. This could mean that there are mispricings in the market that could eventually hurt the buyers of index funds. Index funds are still regarded the best choice for a long term passive investor because of the amount of diversification.