>They say it because in their circles, that's a perfectly acceptable thing to say, and no one would interpret it as anything more than an expression of disapproval. (think 4chan, many subreddits, etc.).

I like how you qualify your statement in regards to reddit by saying "subreddits", which implies that it's only a portion of reddit that demonstrates such behavior, but make no such distinction about 4chan, which, contrary to popular belief, does not solely consist of /b/, and in fact has a number of boards that are actually quite civil.

That said, your point is valid, and, as a regular of one of the more vitriolic boards, I sometimes forget to "switch modes" so to speak, and find myself acting in the manner you describe. My anecdote, for what it's worth.