If as the atheists say we're all just biomass and the sole purpose of life is to do what's in our genetic code, plus that morality is subjective and we should just do what everyone feels is right, why don't we do what is natural, kill those we don't like, take their women and sell their children into slavery?
In essence; if morality comes from what "feels right" and making people I don't like suffer "feels right" then why care about the wellbeing of anyone outside my close kin group? Why compromise to anyone outside my tribe? Why follow social norms that do not benefit me nor my kin?

>Inb4; you heckin' psychopath!!! Morality is a thing because... BECAUSE IT JUST IS OK!!!?!?!