Probably the same reason doping is banned in sports. There's a threshold in the number of people using performance-enhancing substances, that causes it to stop being a choice for the rest of the people, and the situation becomes worse for everybody. A new baseline is set, and if you're not on them you can't compete. Something like that happened in pro cycling:
"Armstrong, on the other hand, was a cyclist competing at elite levels during an era in which doping was rampant. And in such a setting, it does at least arguably matter that “everybody does it.” It is an unfortunate fact that in the world Armstrong competed in, for every individual cyclist doping was a necessary evil, a way of keeping the playing field level. Any cyclist not engaging in doping was effectively relegating himself to the back of the pack. That’s not an excuse, but it’s an accurate description of the facts of the case. So doping was, in a sense, non-optional for the elite cyclist trying to do his job properly, because after all his job is to try to win." - https://archive.canadianbusiness.com/blogs-and-comment/lance...
Now I fear something similar is happening at schools, as children get overdiagnosed with attention disorders. When I was small, I think it was better accepted as a fact of life that it was hard to make children sit still in a traditional school setting. Instead of fixing school, now we are trying to fix the children with drugs. In a setting with lot of medicated children, tolerance for previously deemed normal child behavior is diminishing. Parents freak out if their child isn't behaving as well as his/her medicated peers.
Yes, this is troubling. I'm generally not against medication, but giving it to children without exactly knowing how it affects their personality long-term is a very gray area.
"Armstrong, on the other hand, was a cyclist competing at elite levels during an era in which doping was rampant. And in such a setting, it does at least arguably matter that “everybody does it.” It is an unfortunate fact that in the world Armstrong competed in, for every individual cyclist doping was a necessary evil, a way of keeping the playing field level. Any cyclist not engaging in doping was effectively relegating himself to the back of the pack. That’s not an excuse, but it’s an accurate description of the facts of the case. So doping was, in a sense, non-optional for the elite cyclist trying to do his job properly, because after all his job is to try to win." - https://archive.canadianbusiness.com/blogs-and-comment/lance...