As far as brain imaging, isn't the causal effect in question? I believe that some have asked whether or not being transgendered causes the brain changes or vice verse. To prove one way or another, you would have to examine a large population, at an early age, identify those whose function differs, then follow all to see if that does in fact identify a transgendered individual. I don't believe that that has been done yet. So the results remain interesting, but not compelling one way or the other.
Now, as for being in the DSM I have mixed feeling. I understand not wanting the "you're wacko crazy as sh**" argument. It is unfortunate that all mental conditions have such a negative connotation. Over the last 20 years drugs have been discovered that actually treat the underlying causes of many mental illnesses and treat the problem rather than just control the patient like the old ones did. Does that make it a Medical problem? The argument is being made, by some today, that all mental illnesses are physical at the most basic level. It is just that some Doctors have been given further education useful in treating that grouping of conditions that have a certain aspect. The DSM is a TOOL used by those doctors to help identify and treat those conditions. In our current society, most transgendered people have concomitant socialization problems. I have in the past suffered clinical depression, SAD, GAD as well as GID. Therapy, for me, involved treating All of these in a holistic way. By a shrink. I doubt if a medical doctor would have taken the time to treat that way. Don't they have a 10 minute rule? Hopefully, younger people will have better integration with society and fewer adverse responses to the horrible social stigma we older girls faced. That day, it won't need to be in the DSM and you'll just see your endocrinologist once a year, they will be primary and not an adjunct to your therapist. But for now, I personally believe that for most of us, it is listed in the proper manual and is being treated by the most appropriate medical professionals. Of course, I may be wrong.