Isn't it much more likely that cannabinoids are poisonous to insect larvae?

Interesting because nicotine in tobacco evolved to ward off insects as well and that's why there's so many pesticides made from related chemicals: neonicotinoids.

I'm sorry but that sounds like "wet pavements cause rain" to me. The naming need not be causative in that direction. I'm not disagreeing with that we did indeed evolve with them.. Grug smoke plant. Plant make strong, heal. Grug stomp stupid weeds and make more space for plant. etc

Mushrooms have been around longer than we have, but that doesn't mean they've been making psilocybin that long.

Just because we have receptors that have affinity for molecules that we call cannabinoids doesn't mean much in terms of evolution related to plants. There is a wide range of molecules that have a shape that bind to the wide range of receptors that are a part of what we call the endocannabinoid system.