This is fair enough, and perhaps salient to the issue, but I don't think the same limerick modified to include an Asian female killing herself because she was shamed by sleeping with a 'white' male should be restricted. It would be in poor taste, but worthy of this? How about a Catholic for sleeping with a Muslim? I haven't even seen the limerick, but I would have to say that your point, though well taken, doesn't really change my mind. I would like to think, as someone who doesn't grave offense at such things, that I would likewise not be offended at 'white men have small reproductive organs' jokes. Actually, since I have seen such jokes in cinema and in print and *not* been offended or angry, I guess I do more than think I wouldn't take grave offense. I'm certain I wouldn't.
There are no stereotypes about white men pretending to be Asian to get Asian women into bed, nor do white men face the threat of violence from Asian women who suspect them of passing themselves off as Asian to trick those women into bed. The idea that trans women are 'really' men who are 'tricking' people into thinking they're women for some nefarious purpose is fairly common, and trans women are frequently victims of violence because of it, sometimes killed.
Similarly, white men do not have to worry about being murdered because of a common belief that their reproductive organs are small. Trans women do have to worry about being murdered because of a common belief that they're 'really' men trying to trick other men into bed.