Go forth and multiply

[Philippus Flavius Homovallumus]

Or getting stone drunk, or smoking cigarettes, or driving recklessly, or ..

Nah, humans clearly have a self-destructive streak that is in no way linked to survival. The balance is different in each individual, but it's there.

Go tell that to homosexuals.

Well, I don't know. You could look at the self destructive streak as a way to weed out the weak.