I think and learn so much more on these boards than I ever did or do at school.
Thats interesting Helm, but I can still see how a genetic mutation could answer your gap in that philosophy. A part of evolution is the destruction of individuals with self defeating tendencies. I'm sure there had to have been many instances of humans reasoning themselves into self destorying acts. Subsequently their self defeating habit would no longer exist.
By setting yourself on fire you have effectively prevented overall destruction. If you mate and your tendency for lighting oneself on fire was to eventually diffuse into our whole race, societies and communities would grow to accept self destruction through fire as natural and instinctual, leading to a lesser safety.
But because of sentience you can avoid your urge/reasoning and mate anyway without destroying yourself, so its up to you wether or not the trait will diffuse. I like studying the effects of sentience on evolution. there seems to be little or no data on it.