If Marijuana were legal there'd be no gateway to harder drugs. As it stands now those who sell pot illegally most likely have access to harder drugs too, or they know someone who does. IMHO, lumping pot into the same category as harder drugs only increases the likelihood of someone "graduating" from weed to something far more dangerous.
It's not about who's selling so much as those who are doing no longer being satisfied with how they feel and wanting bigger and better high, or to forget more.
Everyone has there opinion and I'm not trying to push mine here. As I said it's just my opinion and I don't think legalization is right. I don't dislike people who smoke, I did for a long time and I didn't like how it made me feel and act so I stopped.