The big problem with that concept is, that everyone gets lumped into either one extreme or the other. Just like so many other things, there's a huge gray area in the middle, and not everyone who has gender identity issues will suffer from significant distress or impairment in social, occupational or other important areas of functioning. I'm sure that I'm not the only one here on these boards that doesn't fit that description; yet, I don't ever feel quite right as a male, either; there's always this vague feeling that something's not quite right as I go about my day to day life, living and carefully behaving ONLY in stereotypical male ways, never letting any feminine anything show to the rest of the world. It's definitely GID; but it does not impair the rest of my life, nor make me so miserable that I can't function.
Just as previous generations of mental health professionals used to think being homosexual was a disease state, there WILL be changes made in it's definitions in future iterations regarding GID.
We've made progress, but we're not there yet; mostly because far, far too many in the mental health field stop learning when they step out of school, because now they have their masters/doctorate, and then of course believe that they know everything.