Drugs aren't ALL THE SAME, though you wouldn't know sh*t about any of them or how they work so how can you comment? You can't, you know what you react to...the stigma, and that isn't your fault...it's just all you know.
I think people understand the semantics. A drug is a drug is a drug; as a matter of definition you're very right.
In practical terms though - 'bad' drugs are bad. Other drugs that are 'worse' are worse, but this does not make the merely 'bad' drugs any better. If you're going to assess the danger of something, you don't only compare it to something else that is dangerous, it doesn't tell you anything meaningful.
It's also likely true that other players are getting similarly drugged up but just haven't been outed. All well and good, but does this excuse Johns? It sweetens it somewhat with a little perspective, but does it actually excuse him relative to himself? You don't get off a murder charge by arguing that people have murdered in the past. The fact that he took drugs - regardless of how heinous they are - remains fact no matter how many players also take drugs. And that isn't reacting to stigma and treating the word 'drug' as a loaded term meaning all things evil; it's just a statement that Johns took drugs.
As far as the comments on others' drug knowledge goes, it's a bit odd. It appears you're generalising as much as you believe others to be and assuming a good deal. Oh I love the internet.