4th idea:

Once a certain gang has been shown to be violent, membership to that gang should be illegal. A gang is like a corporation. If a corporation was found to be repeatedly sponsoring terrorists I'm pretty sure that company would get shut down and all of its directors jailed.

The same thing should happen to the Hells Angels and any other visibly marked gang with gang members. All the members should equally be held liable for the worst crimes their gang has committed just like all directors would be held responsible for having their company break the law.

Gang members in prison should then be separated and socialized rather than locked up with other criminals because it is a lack of a familial structure that usually leads them to want to join a gang to begin with. The psycopaths should be separated from the others as best as possible, but the regular ones should be given a chance to resocialize.

Have them work raising animals or something. Maybe they could incorporate animal rescue shelters into their prisons or something to give them a chance to learn how to care for things. Or maybe that won't work. Any ideas?