I think it's a mix of people using it as hate speech (because those people always exist), people taking it for hate speech (people looking for anything they can mentally manipulate to make it look like an attack on them), and political correctness (way too many people seem to think that the trap/otoko no ko concept inherently has a transsexual connotation and just because they're physically male and dressing up like girls and acting effeminate it means they're transsexuals and clearly must be viewing themselves as women). The extent of it is quite, well surprising imo. Just a day or two ago saw a moderator on ANN editing someone's comment because he used that term, citing that that term is no longer allowed because of it being "hate speech."
The term "trap" is inherently rooted in a very self-centered, straight male worldview that views any possible 'perversion' of their sexuality as harmful and diminshing. "This person looks like a pretty girl, but they aren't really a girl, ergo they must be trying to 'trick' me into being attracted to them/having sex with them."
In comparison with "trap," which derives its meaning entirely from the feelings of the spectator instead of the person being labeled, 男の娘 is an undeniably less offensive term imo.
