Researchers studying sociopathy often put the number somewhere between 2-8%, with variance seemingly driven by cultural and other environmental factors. Whether or not you believe that sociopathy is a distinctive
thing, it's hard to dispute that a not insignificant subset of human populations are primarily restrained by deterrence
alone--specifically the threat of punishment. That doesn't mean such people are evil or intrinsically violent, they're just opportunistic to the point of almost being mechanically opportunistic.
I'm a glass is half full kind of person so I see factors like empathy as a defining characteristic of humanity, but even I can't deny that such internalized inhibitions, biological and cultural, which mute anti-social behaviors aren't universal.