I think it is every single person, from every walk of life, from every political ideology, that is susceptible to what you described. It really depends on the topic. Sometimes, perfectly reasonable and educated people (politically) lose their minds over something that they are deeply married to. Instead of adjusting their perspectives in the face of new evidence, they double down.
Most people would like to think themselves intelligent, educated, and reasonable. Most people. But most people also hold political beliefs that are to the point of dogmatism or religion.
For example, one of the most educated, reasonable, and intelligent people I have ever met becomes an absolute lunatic when you bring up any weaknesses with the Georgist Tax system (the “land” Georgist system).
My dogmatic rigidity? Probably my opposition to the USA’s unending wars. I get irrational and dumb because I hand-waive any argument and said, “So what, end them all. Bring all our military home. No excuses.”
You: Here is a known propogandist to counter your mountain or reputable citations.
Me: You’ve got serious problems. Here’s the mountain you didn’t address.
You: How dare you! You hypocrite!
K.