A free society can only exist if force is used exclusively in response to harm an individual is actually inflicting, never in response to theoretical harm he might cause.
This distinction between ‘is’ and ‘might’ applies in all situations, from carrying a gun to driving a car to using drugs. Yes, a person with a gun might shoot someone, a person driving might cause an accident, and a drug user might steal to support his habit. The key, though, is that in each case, he also might not, and he must be given the liberty to live as he wishes unless that ‘might’ becomes an ‘is’ and he actually is hurting someone other than himself.
The preemptive initiative of force is never justified, no matter how much you may dislike or disapprove of another person’s actions. Unless he is hurting someone, you must not infringe upon his liberty.