Science can put a lot of these fallacies to bed, that is, if you care about the truth and stuff.
Scans have shown that the TG brain structure is more similar to that of their preferred gender than their natal gender. So, no, it's not all plumbing. TG is a thing. The AMA and APA recognize it. Transitional care has been widely deemed a necessity, and that includes surgery. Insurance companies are covering it.
Being TG is not mental disorder. It's a biological issue. Gender dysphoria is the distress and anxiety that comes with one's natal gender not matching what is organic to them. And it's the external pressures, harassment, discrimination and abuse that intensifies this to the point of depression and suicide. This is not new.
$84 million on ED treatment, guys. $84 MILLION. It's not because you need a boner to fight wars. It's because your junk is your manhood. That's it. That's all. Nature decided sexy time is over for you but you guys aren't whole without wood. So, men with ED are often distressed, anxious and depressed. Sometimes, they're suicidal. You know, "mentally ill" and "unstable". Yet they serve and the military is paying for their treatment. And it's 10 times the cost of TG transitioning treatment, at $2-8 million.
Finally, these people have been fighting wars and peeing next to "normal" folks for ages. No one noticed.
So, there is no legitimate reason to ban them. Trump's announcement is nothing more than a pretext for discrimination. He's sucking up to the Christian right, pulling focus away from his chaos. Nothing more. It's not likely to work in his favor, but he's already succeeded in thrusting the LGBTQ community back onto the stake for burning.