Actually, it makes sense in context to most native English speakers. "To reply in kind," is an oft used idiom. In this phrase "kind" is a synonym for type. It is to say, "to reply in the same way." (Usually in a way which is not kind in the kindness sense.)
http://dictionary.reference.com/browse/retort
I would agree, however, that one, "has no obligation to react to idiotic comments in kind." I hope I've succeeded.
sure, that's absolutist and not always the best response, but not feeding trolls is a tenet of most successful online communities.
I have a ton of respect for Linus Torvalds' technical abilities, and for his way of succinctly and clearly explaining what can often be difficult concepts. However, his off-the-bat lack of civility -- hell, active hostility -- disgusts me sometimes. I'm sure he doesn't care, though: as he said, he's managed to accomplish his goals on the internet just fine how he is. So that's fine, I suppose. I just find it disappointing.
At any rate, there are plenty of examples (no links offhand, but I imagine they're fairly easily googlable if you're curious) of lkmk exchanges where Torvalds is flat out rude to people who are clearly wrong, but, from what I can tell, at least behaving civilly up to the point Torvalds blasts them.
Regardless, though, I still would argue that even in the face of an idiot slinging insults for no reason, "you're an idiot" is a waste of energy and not particularly respect-worthy. Don't feed the trolls.
There's also another attribute of the smartest people I know: they tend to interpret other's responses given the most intelligent interpretation possible.
In the case of some, though, complete neutrality is the best one can do.