I personally don't care what it is, I just know that I'm male and this body isn't. If you want to call it an identity, fine, if you want to call it a medical condition, also fine by me. However if you want to tell me that it doesn't exist, that is not fine. (Just to clarify so I don't cause an outburst on this potentially volatile subject, this isn't aimed at anyone here, just at the world in general. I do that sometimes.)
If I had to pick between calling it an identity or a medical condition then in my case I feel that it's a medical condition. I don't identify as male, I am male and there's a fault in my body. Depression is a medical condition and no one questions that, but it can't be tested for, just like transsexualism. Also like transsexualism it is very real, yet some people have been given the power to 'gatekeep' over who gets treated and in what way, and similarly people choose to treat it in different ways. Some people medicate it, some look for other ways, and each way is just as valid as the next, because no one option is perfect and everyone is an individual.
That's not saying at all that it's okay for 'gatekeeping' to happen. It's really not. And it doesn't work. It's not that difficult to lie to a therapist/councilor/doctor/whoever and tell them what they want to hear to get a certain end result. I lied my way out of counselling for depression numerous times although if I had been honest I would have gotten help off them, but the end result I wanted was to get out of there because he was a twisted sadist. I knew people who had been affected less than me and they were being taken seriously, and even put on anti-depressants, but my goal was just to never see him again and I got that. I could go to a doctor and tell them that I was 100% cisgendered if I wanted to, it would mess me up but it would be possible, so clearly a cisgender person could be allowed through by the gatekeepers if they so desired, rendering it pointless and overall more damaging than good. Also not saying that therapy isn't helpful for some people, but just saying that they shouldn't be given the right to say yes or no.
Overall though, I don't think it matters. We are what we are, and we'll probably never find out why. Does it matter that we don't know why? Not really, it's not going to give some spectacular cure, the best case scenario is if they discover a way to tell for sure in the early stages of a kids life so they don't have to go through the puberty from hell, or to prevent it happening in the first place. I'm not sure where the latter would leave non-binary people though so maybe that wouldn't be so good. I don't see why people get wound up about it, maybe calling it a medical condition will make it easier for people to believe that it's real, but it's not going to make all our problems go away.
As for if there was a medical 'test' discovered for then unless it was severely flawed the only people it should weed out are those for whom transitioning was never what they should be doing in the first place. And they do exist, some because they're pricks who think it's 'cool' -- hopefully they get stopped before they can do irreversible damage to their bodies -- but also people who have underlying mental health problems and they interpret these wrongly. I think the feeling of 'I'm not trans enough' is what scares people most about such a test being discovered, and that seems to be a fairly common, but illogical, thought. I know I've thought it before (but I think I scrapped that a couple of days ago when I cared more about the fact they immediately called me 'young lady' after a motorbike crash than the fact that I'd been hit by a van. I doubt anyone who wasn't really trans would think that a midst so much panic, shock and pain.)
I just have to back and reiterate my overwhelming feeling of, frankly, what difference does it make as long as we get treated how we need to be? Words change all the time, what's 'politically correct' changes all the time (do we call someone who goes to school a pupil, student or learner for example?) and we should just run with whatever the medical professionals prefer that the time to get ourselves the help that we need. As long as it doesn't invalidate us then it's just a term.