The growth in passive funds has caused markets to become more correlated?
This article brings up a point I used to worry about - if people are just automatically pumping money into a list of stocks, how does the price remain connected to reality?.   But apparently the answer is that mis-priced stocks present an arbitrage opportunity (https://www.investopedia.com/terms/i/indexarbitrage.asp), so as long as a few people are paying attention, the price remains rational, and the remaining people paying attention are rewarded for doing so.   The Economist had an article about this issue recently and they concluded that the main effect of Index Funds was to drive low-performance fund managers out of business.