The things children are born not knowing is crazy. The pre-programming is limited ! You have to teach them how to blow their nose. "Don't eat your boogers." Holds finger out to me. I wipe it off. "Don't pick your nose, blow it instead. No, don't pick my nose either."
Is there any reason beyond social standards that you shouldn't you eat your boogers, or pick your nose? And of course children wouldn't be pre-programmed for social standards, because you don't know what region they are going to be provisioned in.
If (say) you're starving to death in Donner Pass, then go ahead. Similar for drinking your urine - if at sea in lifeboat and dying for lack of non-salty water. Otherwise, violations of "eww, ick" social standards tend to be punished harshly.
It seemed really weird for a few years, when conspicuously talking to yourself went from being a "this person has a serious mental illness" indicator, to being a "this person has a cell phone" indicator.