If I had the nerve I would join them. Bad-taste jokes and troublemaking. Badly written manifestos. But I think there are some in the groups who have their heart in the right place and want to do the right thing. And, illegal or not, I've yet to see any other form of western activism that is as disruptive as leaking/hacking.
I think that nails it. These days, the internet is the backbone of our world. There is no form of activism more effective than taking control of online resources, or releasing information.
If a form of activism is socially acceptable it probably means it is not effective anymore. Why go on the street to just get beaten up - and ignored by the media - when hacking is so much more effective in garnering attention for your cause?