No, they’re not. Because drug users actions don’t just affect themselves (I wish it would) but their entire family.
Do you honestly think the government is going to ignore child neglect because the parents are stoners?
Using your logic from above, then the State should regulate everything, because everything you do affects other people in some way. The State could easily use this justification to ban religion, for example.
Just to see if you are willing to be consistent in your arguments, then we should go back to prohibition, shouldn't we?