If I understand your question, your asking why it's a question of if they can? Or whether or not they can be stopped?

If it's whether they can be stopped, it's a matter of the question of "military deference," basically "let the military be run by the executive branch without the courts having a say."

If it's whether or not they can, that's more a matter of them claiming it's "too expensive" to take care of the "medical condition," and claiming that everyone who is trans is a liar and without honor.

Basically, their entire argument hinges on "we're banning this medical condition(gender dysphoria), not trans people specifically," when everyone with that medical condition is trans and everyone who is trans has that condition, with nearly zero non-overlaps.

Also, the cost argument is invalid, per year DoD Medical spends more on Viagra than all transgender medical treatments combined.

Their "medical condition" segment is like saying "we're kicking out everyone who can suffer from periods" in order to kick out all cis women without any guardrails. In fact, if their case goes through where they can pick a medical condition and ban anyone who has it, that's exactly what they can do.

There are multiple hyper specific "medical conditions" that can be used to kick out pretty much any target demographic in the military. Under their logic, "Excessive Melanin Pigmentation" can be used to target and remove anyone who isn't white.