People who sell extremely addictive substances like opiates or cocaine are providing an easy way for people to ruin their lives. I don't think there is anything morally justifiable about making your money getting people hooked on powerful chemicals, even if you do use that money to help fund your sick kid's hospital bills.
While it's clearly up to the individual to make the choice not to get addicted in the first place, its the dealer that provides the temptation, and allows the cycle of addiction to continue. What is the ethics of this? The whole "individual responsibility" argument is often used by dealers to justify what they do and avoid feeling guilty about having a hand in a lot of people's personal downfalls. It just feels wrong, sorry if that's not a good ethical argument.
I am an opiate addict so this may seem hypocritical, and I certainly don't blame anyone but myself for being the way I am.
Compare a weed dealer to a hard drug dealer, and the hard drug dealer almost always is a scumbag who will jack up prices if he knows you are withdrawing, or do some other stuff to rip you off: like say one thing over the phone, then change the deal last minute when you are right about to give him the money so that it feels almost too late to back out. Or telling you a pill or powder is one thing, when it's really something else. (thank god for the internet for that last one) This is using real life examples that I've had to deal with. It might not be true for the hard drug dealers in your town, but that's how it is here. Being a dealer of hard drugs seems to always make people just that much more of a douche bag. Even in the worst periods of my addiction I never sold anything that would be considered a "hard drug," and I refuse to.
I think selling weed or the occasional psychedelic is fine. In the case of psychedelics, the dealer has the responsibility to tell the people the truth about the actual substance, and what to expect from the trip so the user doesn't get totally overwhelmed if they aren't used to tripping. I think a psychedelic dealer has the obligation to ask stuff like "have you tripped before?" and warn about set and setting because those factors are ESSENTIAL when talking about a trip. I can't stand irresponsible psychedelic users that feel like anyone can just take acid or shrooms at any time with no adverse effects.
Weed is just weed. I don't think it's morally right to sell it, but I don't think it's morally wrong either. It's just another commodity. I sold it before, and I'd do it again.