I always want people to be in control of their selves, fully aware of what's going on and what they are doing while they're interacting with others - when they're not, problems can and do happen. Do they always happen? No. But being under a seriously altered state shouldn't be a mission that one aims to achieve.
I don't buy into the concept that "feeling good" means "having an altered state of consciousness" - I don't believe anyone who is a drug addict finds it to be "fun" and, further, I don't believe that they are truly "relaxed."
The "I want to self medicate" argument is the exact thing that will NOT further anyone's efforts to do drugs.
If someone needs to "feel good" by "altering their state of awareness and consciousness" and that is "more appealing that being sober" - they need to seek therapy and learn how to cope with something called "being a living person." It's disturbing that so many people don't want to be in-tune and aware. Is life really that bad? If so - seek help. Have problems - getting high won't fix them or improve your quality of life.
The problem with your position is, not everyone who uses drugs is an "addict." In fact I would venture to say that most people who use certain drugs are NOT addicted to them. For example, hallucinogens, MDMA, and pot; they are fun but not physically addicting although some users can develop a mental dependence on them. Conversely, recall that both alcohol and cigarettes ARE physically addicting, and both perfectly legal.
Then there are drugs which are physically addicting, like the opiates (opium, heroin, morphine, etc.). They are not only addicting but physically debilitating. However, they do require a few repeated uses before the addiction takes hold.
Then you have cocaine (including crack) and Methamphetimine. There is a question surrounding their physical addictiveness, but no question that frequent use is physically debilitating and mentally addicting.
Still, just because you don't buy into the "concept," the fact remains people who use "feel good about having an altered state of consciousness." Otherwise they wouldn't keep using after the first experience. They don't necessarily need "therapy" either. Sober people have their own methods of feeling good, like maybe overeating ice cream, drinking lots of coffee, eating lots of chocolate...all of which can lead to obesity, diabetes, etc.
The point is that everyone should have the right to choose their "poison" and then live with the negative effects, if any. In many cases with the non-addictive drugs, as the OP states there really isn't much downside.