I think we're nearer to the heart of the issue now. You say that the majority of alcohol users are responsible. The assumption is that, conversely, the majority of drug users are irresponsible. However, is this borne out by the facts? I would argue that to determine whether this is true you would have to compare the total population of drug users (which I think we can all agree is larger than we know) to the percentage that commits other crimes (robbery, domestic violence, etc.). If the comparison yields numbers equal to or higher than that found in alcohol users, the argument that drugs are simply too dangerous to permit may have some merit.
I don't have the stats at my fingertips, and I don't even know that accurate data exists to make this comparison. My point is simply that our information about drug users, especially in the mainstream news media, focuses on those users who do commit other crimes and otherwise make an utter mess of their lives. Is this because they truly represent the majority of drug users, or is it because they're the ones getting caught on account of their stupid, self-destructive behavior?
From personal experience, I have known and witnessed many hard drug users. I have not known one single HARD drug user that I would have said was acting responsibly and with reason while high on the narcotic, at any level of use. Whereas with alcohol, only those who consumed VERY VERY high amounts of it, were acting the same way.