It seems to happen due to your views being strongly tied to your identity, so every time someone tries to disprove your POV, people feel like someone's attacking them personally and tries to undercut their whole life.
Indeed. Identity, ego and a sense that these things are real enough to protect or die for. Quite strange considering that they are psychological constructs that change heavily over time.
The problem is that people treat illusion as real. All it takes is that assumption. And it has very dangerous consequences!