The film describes the radical organization with the same name.  Here is some background:

http://en.wikipedia.org/wiki/The_Weather_Underground

The film uses interviews with members, which is an interesting touch because it gets right to the source.  At the same time, the members discuss their reasons for supporting violence.  (See the quotes on the link)

We felt that doing nothing in a period of repressive violence is itself a form of violence. That's really the part that I think is the hardest for people to understand. If you sit in your house, live your white life and go to your white job, and allow the country that you live in to murder people and to commit genocide, and you sit there and you don't do anything about it, that's violence." Naomi Jaffe

This is an interesting perspective, but it really helps explain their thoughts.