> I can't imagine any connection between identifying plants and having the introspection and self-criticality to know if, when and how much of a psychoactive substance to use.
So the precedent I'd cite is with Hindu ashrams, where they're not going to impart any sort of esoteric spiritual training unless you're already brushing your teeth every day, keeping your room tidy, can hold a job, etc. The connection is that a lot of the higher-level practices can be profoundly destabilizing, so ensuring that people are continually performing the baseline tasks necessary to be a semi-functional adult is a good way to reduce the likelihood of people completely losing their shit.
With mushroom identification you need to join a community of likeminded people, put in the time needed to learn, scout the correct terrain, go to the right place during the right weather conditions, etc. It's not super complicated, but it's a good baseline to weed out the sort of people who become statistics after eating a handful of random drugs without knowing what they are, the dosage, the expected effects, etc.
Whether it's making people pass a driver's license type test, making them identify the plants or fungi in the wild, making them extract or synthesize the substances themselves, etc., I think the best drug policy is policy that allows anyone to consume any substance but which discourages people from impulsively swallowing handfuls of random stuff.