Exactly. You can't expect people to act in a relativist way when they have absolutist beliefs.

That's the first thing to recognize.

The second thing to recognize is that people's beliefs are largely based on their group / tribal affiliation, and are often performative and approval-seeking.

So there are two things we can do.

First, we can offer thoughtful, logical objections to their fundamental beliefs. This may seem hard, but I've seen several ex-Christians (even on Medium) who say that they were able to leave their faith because of someone who posed insightful challenges to their beliefs.

And the second thing is to not demonize them so much. Each individual Christian is just a person who is trying to survive in their community. They believe what they've been told from the time they were a child. It's a hard thing to step out of. Perspective is a hard thing to broaden. The same reason why you may thing they are evil to the core is the same reason why they think the same of you. The only way to convert people away from their current tribal beliefs is to offer a pathway into a new tribe - which won't work if you just call them evil.