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How is this anything but a non-sequitur? Personal attacks aren't ungrammatical and racial slurs aren't ungrammatical. Yelling "FIRST!" at the top of a comment thread probably isn't ungrammatical either. Like using 'he' for a generic user, each behavior is obnoxious (albeit in different ways and with different scales).

Singular they is well established as a grammatical construction (http://www.crossmyt.com/hc/linghebr/sgtheirl.html, for instance), and avoids the issue entirely.