Public Opinion Question about the Hells Angels and similar Motor Bike clubs/gangs?

I recently read a book about the Hells Angels, that covered various countries and numerous allegations [and convictions]about their strong arm tactics, including trafficking drugs, murder, aults and organized crime. So, if the general public know that these biker gangs/clubs are conducting behaviors that threaten innocent members of the public and these that get involved way-over their heads in these gangs/clubs criminal activities 'why doesn't the authorities simply ban these groups as they have with terrorist organizations and arrest them for their ociation". Clearly if the roles where reversed and the bikers thought that another club had done something against their code, they would punish them without fair-justice or right to appeal.