Why is everything evil?
The people you see doing that aren't being rational, they just say those things to blame someone. Wall Street is evil, but they use their services. Walmart is evil, but they go there and buy.
The most important thing about those claims is the sentiment behind them. The sentiment is that Wall Street led US into a financial crisis (which it did, even though it's just a piece on a chain of causes).
There are a lot of problems concerning Wall Street, the government (and the political system in general) and the corporate world, that affect people. Better have people speaking out non-sense than doing nothing, at least those in power know people are getting angry and revolted.