They change the equation when someone is advocating for “full legalization” with (sometimes) “no government regulation”. The argument is (rightly or wrongly) that certain drugs are actually so harmful that they should be kept out of the public.
Yes, that's what I was thinking. They are so destructive and addictive that people can't stop taking them. I worry that if they were legal and cheap people would get hooked on them and cause a lot of devastation ton themselves and their families. Of course there are people today who can't get methadone to treat their heroin addictions, because of legality concerns where it's not available.
Alcohol causes tremendous destruction, too, but I thought there was general agreement that national prohibition was worse.