Here is the argument in a nutshell (if I read it right): (1) The economy not really working that great even though it is working as intended. So it cannot be fixed, because it is not broken (2) For businesses to create new value, they need money. It used to be that they could make their own money, get moving themselves, but now things are dominated by bank lending. (3) Bank lending relies on continual economic expansion to work. (4) But economic growth is going to plateau, due to lack of new things to exploit (i.e. situation similar to lack of new countries for the Roman Empire to expand into). (5) There are alternative money systems that let people create things without bank domination. (6) The political Left is not savvy to this. If you want change you should push for support for alternative money and vote for such candidates.
It is hard to get what people are on about when it comes to anti-bank sentiment. But then again, one could say the same about free software. Seems like the kind of thing where one has to do a bit of their own research and their own thinking.