I see a lot of issues here
You are conflating the general notion of index funds with the common investing advice of buying and holding index funds. I would argue that holding here is the vast majority of the advice. Plenty of people day trade index funds. You should be explicit that your objection is to the un-informed buying and holding of index funds. Also, you should be explicit in how you think a crash would come about, instead of simply mentioning a popular investment category.
Index funds do not discriminate. I don't understand how you drew the connection between them and an individual company like Amazon.
You make the assumption that people who now buy index funds would otherwise be intelligent investors that would correctly set stock prices. I doubt it. The trading patterns of most people have to be near random, more noise than signal, and likely very emotional. In fact, in this way index funds reduce the chances of a crash by removing this kind of nervous money from the stock market.
You make the assumption that index funds would swallow up all investments when in reality the edge that active investors have increases as the number of active vs passive investors decreases. There is a self-balancing force at play.
You simply have a wrong outlook on index funds. Buying a total index fund is investing in the entire stock market; betting that it is healthy and will grow with time. That's all. It is as much "too good to be true" as a healthy economy. Yes, buying an index fund means not participating in the process of correctly allocating resources to the best companies. But the important thing is that you are not in any way harming the actual participants because you obey their prices. This means you are essentially investing as the average active investor.
And lastly, it is naive to think that "fat cats" take more money from passive investors than they do from active ones.