Why are bikie gangs outlawed?

Your wrong and naive ! Hells Angels are into drugs, prostitution, guns, murder, stealing, killing, intimidation, extortion's and anything for a buck. No rules, and they contribute ZERO NADA ! To as/a the benefit of society. they cheat and undermine everything. Even taxes ! They are cut throat pirates & renegades, mercenaries on bikes [motorcycles] so they can out manoeuvre the cop cars. you can go almost anywhere on a bike.