The left is on average higher IQ than the right. Not by a lot, but enough that it's something they're proud of. As a result there's a protective status barrier around their ideas - if you disagree you get lumped in with the "dumb people." Many disastrous consequences follow.
It's a myth about the frog. If you heat up the water it just jumps out. If you mistreat a caged tiger it will maul you. Modern humans are unique in their capacity to tolerate abuse without fighting back.