How do angry, hateful, vicious people like MTG convince themselves they’re Christian?

I don’t think it’s a pose - she appears to be entirely sincere about her claim to Christianity.

And I understand the basic mechanics of it - they pick and choose which parts of the Bible to highlight and which to ignore, and how to self-servingly interpret the ones they do pick.

But in a more fundamental sense, I still don’t understand how they do it. Are they really entirely devoid of self-awareness or conscience? How is that even possible? Or do they have at least some rudimentary self-awareness and conscience, but they just ignore it? How is that even possible?