Getting back to volver’s original question,
‘Why do people take these attitudes? Is it just an attempt to make life simple in their minds, when it's anything but?’
I think that is what it is. Some people are interested/involved, and are open minded to learning from what they read and from others, so have a lot of knowledge That can make them come across as pedantic or confrontational, when often it’s frustration because others don’t/can’t take their valid points on board.
Other people are more focussed on other things, less interested in the wider world and the detail of what makes it tick, and they are more likely to take information on face value and (sometimes, not always) exaggerate it.
I think, it’s really about people’s different interest in/attitudes to the world outside their own sphere of knowledge and influence. Their politics actually has very little to do with it, it’s just a convenient hanger.