Your welcome to believe that it is bad for you and that you don't want to do it, but I disagree that that should translate to you saying other people can't do something.
We could easily replace pot with any number of substances, even legal psychoactive drugs. There are plenty of alcoholics in this world, does that mean that if I can enjoy alcohol occasionally and responsibly I shouldn't be able to? Many anxiety patients abuse their benzodiazapines, should patients that follow prescribed treatment and benefit from them also be made into villains?
I'm sorry for anyone who becomes dependent upon anything and hope they get help, I have experienced it with members of my own family. I'd like to think that a legal structure and clear education would help (though I don't recall in High School ever being given any instruction on responsible drinking, which should happen in my opinion). But some of us benefit from smoking within reason, from indulging in the rare psychoactive break from reality, that some people have problems with these things - doesn't mean everyone does.
Edit: I realize in the opening I use "you" saying other people shouldn't do it. In your comment, you don't make any explicit mention of supporting prohibition, and was using you there in the plural sense, apologize for the comment.