[spiffytech]

Even when someone gets exposure to a competing viewpoint, it's rare for them to really give it thought if the topic is important to them.

People build their identities on what they believe about the world or on which people (dis)agree with them.

When their belief (and thus their identity) is threatened, people readily perform whatever mental gymnastics allow them to continue believing they're in the right.

The excellent book The Scout Mindset covers this in depth.