The question should be: Why should anyone have the right to tell someone else how to live their life when the only "harm" that someone does to others is get bigots, snobs, and social dictators angry?
Most often its the religious conservatives the ones that make up these wild fears about the "consequences" of "deviant behavior" that turn out to be unfounded, look at what they accused everyone from rock n roll bands in the 50s to gay people nowadays of, that turn out to be BS / baloney.
People that hate transgender people have a problem with themselves and most likely are often irritating / annoying / judgemental ->-bleeped-<- type people in general, In other words, its their problem, not ours.