Construct an argument - defend your position - and so on. This thought was brought to you by a man with a huge track record of point blank refusal to put up evidence when asked.
Okay, well let's go back a few months ago when you were making that demand on me - that I should present evidence of what I was talking about. In that case what you wanted evidence that wanting to be another gender (or 'transitioning' to another gender) was in fact a mental illness all on its own and not just something that could be fixed by hormones/surgery.
Some thirty or forty years ago there was absolutely no debate in psychological circles that wanting to be another gender was a mental illness. It actually had its own name - 'gender identity dysphoria'. People who expressed that desire were treated as though they were crazy and were given psychiatric and psychological treatments to try and help them accept the gender that they were born as.
Fast forward to the present day and you'd be in all sorts of trouble if you labelled someone who was 'gender confused' as being in any way mentally ill; there's a huge push to normalise people who feel that they were born into the wrong gender identity as if they have an intrinsic right to be the gender that they want to be and not the one that they were born with. Now as I recall you were asking me to present you with direct evidence that people who were gender identity confused as mentally-ill.
Obviously, that statement in itself is extremely simplistic and it doesn't encapsulate the whole range of people who are in that category - some of whom will obviously be made 'whole' by 'transitioning' into their preferred gender identity - and some of whom are not going to be 'cured' by doing that. Some of that cohort are just plain nuts and part of their pathology is presenting with that 'gender identity dysphoria'.
All that debate aside, your asking me to present an argument that gender identity issues are linked to mental illness is a massive task - like trying to explain the nature of existence in one paragraph. And there's no definitive answer - none at all. Its one of those things that can't be encapsulated easily and there's (obviously) going to be a lot of evidence either contrary or supporting either one of those positions. That's not counting the fact that what is considered normal and what is considered pathological has changed with time and (dare I say) fashion.
Are you beginning to get where I'm coming from? I can't possibly provide all the answers, all the evidence, all the research - to every single topic that we discuss here. And I certainly can't do that without offending some people - which I seem to have an easy ability to do.
Do your own research, come up with your own answers and present them here for discussion (preferably with links but I don't care if you link or not). That's the answer.