That's a really good question. I don't think there is anything inherently evil in using drugs to change your state of mind. It depends on circumstances. I get a little buzzed off too much wine sometimes, and that's OK.
I would never deny anyone's right to self-medicate, even if I thought they were wrong. I just disagree with the medicalization of behaviors and I think that belief system does have detrimental effects.
Also, we are starting to hear about the long term effects of Ritalin, and we'll probably learn more about that. Although the parents should be responsible for these decisions, most of them believe what the doctors tell them and think they are treating some disorder.