The problem is, Self ID means that men don't have to do any of that (removal of said testicles), just self declare as a woman, sign a form and hey presto - are supposed to be legally accepted as women for all purposes. The vast majority of transwomen (i.e. biological males) don't undergo any surgery.
This is obviously problematic for women, and is why there are male rapists with full functioning penises in women's prisons, males competing in women's sports etc.
If you think it would never happen, it's already happening.