They are expressing grievances not only against the banks but more importantly against the blatant income inequality in the U.S., with the 1% ultra-rich paying less of their fair share in taxes while the downtrodden low-income masses bear more of the burden, even as massive unemployment has made their lives more unbearable.
The most blatant account of this was when in December Ron Paul was only give 87 seconds out of a 2-hour debate, despite polling in 2nd place at that point.