The Motorcycle Profiling Project provides statistics to show that criminality is not actually all that common among "Outlaw motorcycle clubs," in spite of Federal arguments to the contrary.
I understand that the name must be confusing. It's like Outlaw Country music, though. Their ethic is about a spirit of rebellion and a devotion to personal freedom more than it is about actually breaking the law. I suspect that, at worst, most people in both communities are more indifferent to whether they violate the law rather than committed to violating it. Probably this is especially true in matters of marijuana use, which is regrettably common in both communities.
Though I myself have never made use of any illegal drugs, and regard them as generally bad ideas, I can see why many people might take it as improper for the government to involve itself in the question of what relatively harmless substances they ingest. I tend to be more focused on the enumerated liberties and rights, which are in grave enough danger where they are not already -- as especially in the case of the 10th Amendment -- being openly violated by the government. In such an environment, being in some sense an Outlaw is the only way not to lay down your freedom.