Robert Reich's "Saving Capitalism" documentary on Netflix does a pretty good job to answer this question.

TLDR; Wall Street is part of an industrial/political system that extols "free market" capitalism, publicly, when in fact, "free markets" and "free market meritocracy" is a myth, and they know it. Privately, these same people hire lobbyists and otherwise influence the political system to craft regulation & policy around property, monopoly, contracts, bankruptcy, and enforcement. These regulations protect and enhance the benefit of the few.

I wouldn't say that's totally wrong... but does it follow that, therefore, there should be no regulation whatsoever? That has negative consequences too.

One that bothers me the most is automated high frequency trading. They can cause the entire market to crash because of one mistake.

automated high frequency trading also does the important work of eliminating the question "Which exchange should I buy AAPL at?"

HFT is mostly ultra-fast arbitrage programs, and the benefit of using them far outweighs the downsides.

Maybe the problem is not with HFT but in the industry as a whole

A human trader can also cause the entire market to crash because of one mistake. See Waddell trading 75k e-minis or PVM trading 7 million barrels of brent while drunk.