I have never equated disagreement with being flamed.

I'd wholly agree there. But there is a difference between expressing disagreement, or responding in a highly critical way, and coming out with a stream of insults which are totally unrelated to the disagreement.   

Som people do seem to fall very easily into doing that kind of thing. And one of the results is that people who don't like that kind of thing can start to assume that disagreement can't be expressed in other ways, and that it should therefore be avoided, even at the risk of blandness.