In America we live in a democracy (last I checked) so it's the mainstream public who decides in the end. The people in various western states were the first to decide that marijuana should be legal. So by normies I mean mainstream voters who worry about their children having uncontrolled access to psychedelics. Normies believe rules are made to be followed and laws are there for a reason.
Legalization would decrease underage availability, if anything.
To quote an older friend who grew up in a dry county in Alabama: “The bootleggers didn’t care how old you were which was a good thing because I liked to drink and when I was 16 I looked 13”