Spice will give you an approximation of a "runner's high" without the tedious mucking about of exercise. There is, of course, an upper limit which too many products tip past.

It can be fun to safely experience sensory extremes. Many people get an endorphin/dopamine rush from it.

Other than some gut irritation it's not a significant hazard. Like yeah keep it safely stored from sensitive people and pets also it's probably not the best road trip snack or whatever. Certainly less dangerous than alcohol, fireworks, cigarettes or texting while driving.

in the past i thought eating spicy food made me look cool and manly, but then i realised i'm missing out on the flavour of foods and understood i was being silly. so now i mostly stick to mild foods, with the occasional spicy food for varity's sake but only if i can actually taste the flavour of said food through the spice

but that's just me

I realize I'm a special case, but my nose is essentially non-functional—I don't smell food. While my sense of taste is more sensitive than your average person, I suspect I still miss out on some kinds of flavour. I believe my impairment is why I am drawn towards strong tastes like cheeses or, indeed, extremely spicy food. They're the "only" flavours that I really experience strongly.

self inflicted pain with no scars or prema damage, as long as it's below pepper spray.

Because it's fun. Live a little.