I almost entirely agree with your post, but I don't think the bit quoted above is really true.

It doesn't seem to me that the reflex to shout "facist!" is so tightly interwoven to feeling challenge that the two are inseparable. I think it still depends a lot on style.

For instance, I challenge everyone all the time--see, here I am, challenging you!--on some aspect of what they wrote because, as you said, there isn't much reason to write otherwise. That's what claps are for. But I can't recall an occasion where I have been called a fascist (maybe it's happened and I forgot--people do make dumb accusations now and then). Mostly it's because I very very much am not a fascist, and secondarily whenever I make a suggestion that is easily misinterpreted as advocating a fascist position, I take extra pains to clarify so that the misinterpretation is even less likely.

Now, it may be that certain challenges that are not wholly unreasonable to raise are, in fact, almost necessarily going to result in such charges. That's fine. But I don't think it just goes with the territory of being challenging.