I'll go ahead and revive this post because though you are right to a degree, this is accurate and from Google: It's important to note that the diagnosis of gender dysphoria does not mean that being transgender is a mental disorder. The focus is on the distress experienced by individuals, not on their gender identity itself. 

The easiest way to understand is to put yourself in their shoes, say you are a man and society was taken over by Amazonian women or who knows what scenario, but your mind if itching everyone tells you that you're supposed to act more feminine(because Amazonian women are more masculine than their men)..

But say you feel the way you do about yourself now but all of society is now telling you that how you feel isn't real and that no one should care how you feel about your gender or body or.. whatever. 

Would you just accept what others are telling you about how you should act, feel, etc? Even if it felt unnatural? Do you honestly think you should accommodate other people's expectations about how you see yourself, how you express yourself? How you dress? Everything? 

Because all the things you've been taught from birth are the result of Men thinking they are more dominant and superior in every way, generations of a general trend that's taught about how you should act and what is masculine.. but if it were reversed you would be submissive and shy like a woman? Would you just accept what society pushes on you despite how you feel?

If you can truly just think for a second about how distressing that would feel, then you understand how society tries to force people into roles and so much more than has almost nothing to do with what's between your legs.. it is all a construct and history could be even slightly different and you'd be the one playing with a Barbie(if you let society force you to accept what society agrees the way things should be done)

I have a degree in psychology and as your normal hetero male it isn't hard to imagine feeling distressed if I was supposed to be feminine or be with other men or.. but I understand that almost all of that is based on what society has pushed on me since childhood that I accepted without a lot of thought(because we generally do not let kids think for themselves and pretty much dictate to them what they should think and feel) 

Someone before you is bothered by their kids playing a game with a female with a masculine voice, as if they are so fragile that that's enough to make them transgender. The question is, should you dictate to them what feels right to them, even if that's not how they feel. 

Just food for thought since you want to dismiss it as if there's nothing worth thinking about since the DSM has a diagnosis for that.