"I have found it immensely frustrating discussing with people who think when I argue with something they say, that I'm attacking them as a person. I'm not. I'm just saying e.g. something they've said doesn't fir the facts; or is illogical."

Yeah! I've been frustrated by that too. I realize that ego isn't always the dominant factor in causing people to argue, but I think it is the dominant factor when they do what you're alluding to above and assume that disagreement about the subject under discussion is a personal attack on them.

Their sense of identity is so strongly linked TO their various beliefs and opinions that if you disagree with their belief or opinion, then their sense of identity seems (to them) to be threatened, and they rush to defend it. This is the primary thing, I think, which has triggered a great many religions wars throughout history. (as well as the usual aim of war: material gain).