And doesn't deter me in the least. Pass the hot sauce, please!

Most of the ones with toxins strong enough to kill you won't do so for months after you consumed it a single time. They know something about playing the long game.

i wonder how a chemical that can distort perception of time and space could be a useful defense mechanism...... harder to find the mushroom when you cant remember where you ate it.

They produce psilocybin because Satan told them to

It's just a guess, but it's probably protection against other species than mammals (psilocybin I mean)...

Regarding capsaicin, it's protecting against (almost) everything that is isn't a bird, birds don't feel the capsaicin AFAIK.