I've thought about this a lot, and by nature of the internet, we have to fill in the blanks since we aren't interacting in person.I think the problem has to do with social media and the internet as a whole bringing out the absolute worst in people, and that includes their "die on their hill" political stance. in a normal setting, I interact with right-leaning people without a problem, despite having largely different opinions on the way the world works.
I feel fairly confident this is similar to how we act with drivers on the road, as well. We seem to 'thingify' people when we can't actually interact with them, and we're very adept at convincing ourselves we are correct about the initial blanks we fill. We can't really have world views without making some assumptions, leaps of faith, and then testing all of it - which is hard to do when we're all naturally inclined to be somewhat stubborn.