All human brains have evolved to resist destabilization … to reject information that detracts from coping and survival. This phenomena (I call it [preservation of homeostasis](https://www.quora.com/search?q=homeostasis%20preservation&author=84795924 “www.quora.com”)) applies most forcefully to core notions of identity and worldview. And what could be more disruptive to one’s worldview and stable serenity, than to recognize that you’ve been raising or dating a highly flawed and violent person?
So we all do denial. Some just do it more visibly and outrageously than the rest of us, so our attention goes them as if they are radically different … and they are not … not really.
But to your point, it’s certainly true that people quite high in denial, are both more capable of tolerating, and more actively enabling, to anti-social personalities.