They're angry and justify to avoid challenging their own worldview. Apart from general evil, that basically sums it up. To expand: Plenty of them are convinced what they are doing is right. They legitimately believe they are on the right side. We don't really see this because we aren't constantly soaking up the same news every single day. We aren't surrounded by people parroting false truths without a check (though we are in our own nodes), and we challenge one another's beliefs, something people leaning left tend to do. For the rest it is about hurting others. A much smaller percentage could be convinced they're wrong and just haven't found a strong enough reason to challenge what they believe in.

None of this is good. Though we will gain the most ground by attempting to be understanding and being firm whenever needed.