When people invest money into index funds, then the funds must spend all that money buying the shares of the underlying fund companies. So that creates tons of buy orders for the underlying stocks, which creates the buying pressure, which makes the prices rise. As long as more money comes into the index funds the prices of underlying stocks will keep rising. But the higher the prices of the underlying the more money needs to come in to buy them at those prices.
What eventually happens is that there's not enough new money coming in for index fund buy orders to maintain the bottom of the underlying prices, which means that the prices start drifting lower, the popular financial press goes nuts, CNBC/FoxBusiness/WallSt Journal/etc blast it in the headlines and the same way goes the other way. People start selling their index funds, which makes the index funds sell the underlying which creates a massive wave of the sell orders creating a downward pressure, which in turn puts brings the indexes lower which makes press go screaming more which causes more people to want to "protect their test egg" by selling the index funds they had.
But this doesn't seem to have anything to do with index funds. Wouldn't the same thing happen regardless of the way people are invested into the stock market?
It is directly related to the index funds. They are now marketed as the "correct" way of invest into the market where they in fact invest into a very small number of companies creating an artificial wave of the buy orders.
Actively managed funds have choices in what they invest, and how much they put into any of the companies. Index funds do not.
A bit more exciting probably since the market is higher now which means that the oscillation will be more impressive.
The rest is chicken little - we got into that mess before because neither CDOs nor CDSs were liquid which means that as long as they were not trading banks were able to continue book them at the nominal value and since to trade them one needed to have banks that were on a hook for them to do the trade nothing was moving. That's the biggest issue with those kinds of instruments.
Nothing of sort could happen with the index funds because both the derivatives and the underlying are sufficiently liquid, so the drop won't be 100->20 but rather 100->99.9->99.8->99.7->....->20.1->20 which in turn would re-balance everything.
What eventually happens is that there's not enough new money coming in for index fund buy orders to maintain the bottom of the underlying prices, which means that the prices start drifting lower, the popular financial press goes nuts, CNBC/FoxBusiness/WallSt Journal/etc blast it in the headlines and the same way goes the other way. People start selling their index funds, which makes the index funds sell the underlying which creates a massive wave of the sell orders creating a downward pressure, which in turn puts brings the indexes lower which makes press go screaming more which causes more people to want to "protect their test egg" by selling the index funds they had.