But it's a critically important minority - it's well researched that CEOs, bankers, and other highly successful types in business have sociopathic traits. (I attach no moral judgment to that - just stating it.) Full, diagnosable sociopathy and psychopathy are rare, as you point out. People with a decreased ability to feel empathy are a minority, but they have a disproportionate ability to shape society.

For that reason, I'm always somewhat annoyed when other atheists (I'm an atheist myself) rely on some shared sense of human empathy and argue from it - it's only convincing in a society where empathetic people wield power. We don't live in such a world. To convince people to act humanely even if they don't feel empathy, we need to appeal to a higher objective source of truth as the religious do, or find an argument for humane acts that doesn't rely on appealing to people's consciences.