The plant has evolved capsaicin as an animal deterrent as only birds can disperse chilli pepper seeds while animals digest the seeds. No other animal other than humans like chilli. Humans are an exception because we cook our food and cooking alters food chemistry in a such way that spices become desirable when mixed with meat or vegetables. You won't be able to eat even 50g of ripe red chillies freshly plucked from the chilli shrub.
Also, there are different species, I've eaten lots of different chili, I've eaten whole raw Bhut Jolokias, that was not pleasant, I didn't like it, it hurt a lot and the taste was not nice either.
Lots of milder species are lovely to eat raw, they have a mild burn which I do find enjoyable, and they have a fresh sweet flavor which tastes great.
"Humans don't like <thing> because they don't enjoy consuming it in some arbitrary quantity"? Really, that's your argument? I'm not capable of eating 1kg of bread, does that mean I don't like bread?
I "like" a thing when I get pleasure out of practicing/consuming it in some form.
> The plant has evolved capsaicin as an animal deterrent as only birds can disperse chilli pepper seeds while animals digest the seeds.
That's a common explanation but the article links to a study that supports another explanation, capsaicin having likely evolved for its antimicrobial properties instead:
It is an interesting study but why would an anti-microbial agent act as an animal deterrent. A goat or a monkey would disperse the seeds if not for capsaicin. I feel that there was some evolutionary pressure for selecting against animals consuming the fruit or else only some animals would feel effects of capsaicin and others would not.
If mortality of seeds by fungus infection is more important than seed dispersal by mammals, then it makes sense to produce capsaicin. Since birds are likely better at dispersal than mammals (and don't have teeth) preventing mammals from eating chilli peppers might also be a beneficial side effect of the production of capsaicin, even if not the main reason for it.
Evolution just works on chance mutations and capsaicin is just what chilli peppers happened to start producing. Maybe if they happened to make penicillin instead they'd be better off, but they just do with what they have and that is capsaicin. They were just lucky that birds and humans tolerate capsaicin.
