It's not just varying levels of hot-ness that distinguishes them but a wide variety of flavor profiles and preparation techniques that enhance those flavors. Some peppers can absolutely be eaten raw and with seeds, others do well with drying and roasting prior to use, others are hot no matter how you prepare them and even if you remove the seeds.
I think the actual heat that folks react to is mostly just an acquired taste and NOT something that's been programmed in by evolution to keep humans from eating these things. You can get used to rather hot peppers, but even if you don't there's many which have a low-enough scoville number (in the 10000's), that the heat is controllable by using less and one can still enjoy the other aspects of pepper's flavor.
>The seeds of Capsicum plants are dispersed predominantly by birds. In birds, the TRPV1 channel does not respond to capsaicin or related chemicals (avian vs. mammalian TRPV1 show functional diversity and selective sensitivity). This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth which destroy such seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it disperse.[6]
It's not just varying levels of hot-ness that distinguishes them but a wide variety of flavor profiles and preparation techniques that enhance those flavors. Some peppers can absolutely be eaten raw and with seeds, others do well with drying and roasting prior to use, others are hot no matter how you prepare them and even if you remove the seeds.
I think the actual heat that folks react to is mostly just an acquired taste and NOT something that's been programmed in by evolution to keep humans from eating these things. You can get used to rather hot peppers, but even if you don't there's many which have a low-enough scoville number (in the 10000's), that the heat is controllable by using less and one can still enjoy the other aspects of pepper's flavor.