I am really not sure where I said that trans men don't require the same level of safeguarding as women, or how that's what you have taken from my posts. Just to clarify - my view is that you are absolutely right that there are many trans men who have suffered past sexual trauma, are neurodiverse, or have other vulnerabilities. Many of them are also young. How we can provide a good level of safeguarding for them, however, is complicated.
'And your answer is to create a space where a man, any man, including every single predator in the land, can access them naked.'
The fact is, these young people go into male changing rooms all the time, because they identify as male. Which throws up the exact thing you're worried about - that they are surrounded by biological males who are seeing them undress.
You can tell them not to do this and shout about biological sex until you're blue in the face, but if you know any young trans men, you will know that most of them don't want to use the women's, and they won't do so simply because you tell them to. If you have ever met a teenager, you'll know they can be pretty stubborn and rebellious, too. They are at risk from going into male changing rooms.
A gender neutral changing space (or ideally a cubicle!) is a much better way to safeguard those individuals rather than them going into male-only spaces (which they will do, regardless of what you say about biological sex).
Safeguarding is complicated, it's definitely not black and white.
What the gym should really do is put in some cubicles.