I don't even think many devs are 'stoners' in the sense of using marijuana daily. I don't think you could code at a high level if you were actually smoking weed every day, but it just feels invasive for a job to tell me I can NEVER touch it and they will monitor me to check.
I am not a huge fan of alcohol, but if a job told me I could never drink again and they will test me to see if I have been drinking it would feel super invasive and be a huge turn off.