Substitute “alcohol” for “drugs”.
Prohibition is worse than the alternative.
So you think society holds individuals accountable for their alcohol related problems? I don't think so.
I accepted your terms for the discussion. Simply disagreeing, especially when I stated the conditions I would agree with you tells me yours was not a thought out response. That's fine if that's what your standards are, but if libertarians are serious about persuading people, you'll need to do better than just shout "Prohibition!"