A suicide rate of 40% is well documented, and there is no solid evidence that transitioning lowers the risk substantially. As for the argument that discrimination accounts for the high suicide rate, by that logic the suicide rate in the black community should be quite high. It is, in fact, lower than the white suicide rate. A demographic with a high suicide rate should be a concern.

Otherwise healthy people who take daily medication for ADHD or mild depression and function just fine with it are barred from enlisting in the military, despite the fact they want to serve their country. People with certain physical limitations or who will need surgery for some medical condition want to serve their country and are barred anyway. So why would someone who must take daily hormones or is wanting/planning reassignment surgery be allowed in when others on medications or who may need some kind of surgery are not?