On meta-level, I find it somewhat ironical that LW community, as well as EY, who usually seem to disapprove of oversensitivity displayed by tumblr's social justice community, seem also deeply offended by prejudice against them and a joke that originates from this prejudice.

Eh, I'm not sure I agree with the first claim. Yes, some people here are touchy, especially about this issue, but many of us are not touchy about this issue (or in general), and to claim that the LW community is touchy seems like an overgeneralization, and I think LWers typically disapprove of the process of overgeneralization, which can lead to conflicts with various social justice claims and narratives.