> alternatives where we would identify and just generally regulate the harmful features

Good point. The age ban is based on the idea that it is worse for kids (and other exploits) when the big idea is that it is bad for everyone, just moreso for kids. Might as well protect the whole populace when one change of the app design will do that.

Alcohol and cigarettes are bad for you but we've decided that when you turn 18 you have the freedom to ruin your own life. (But not with LSD, for some reason)