The pentagons very own report on this indicates that it has no effect on the military's combat readiness or effectiveness. The problem is that you're making this into a political issue. Being trans doesn't necessarily mean being mentally ill, nor do we hold trans people to different standards of behavioral and mental health then we do anyone else in the armed forces. If you get accepted, go through bootcamp, and serve just like everyone else, then your gender identity has literally no bearing on your combat readiness or effectiveness. You've literally boiled down this entire issue to, "I think these people are weird and different, therefor I should be able to treat them differently and discriminate against them for untold, poor, and unproven reasons". Congratulations, you're literally a bigot.