> What about the alternative possibility - the author is a rather intelligent being, but what they've written in this instance is idiotic?

With respect, I think you're doing the same thing. You picked a word to squabble about while ignoring the context of the sentence. If you take the sentence and replace "is an idiot" with "has an idiotic point", my argument isn't weakened. Neither is the argument in the original article: we make this assumption more often than we should, because the game we choose to play is to be the smartest guy or gal on the internet.