Let's assume the following for a moment:
- a person grows up as a man, with the matching hormonal profile for his first 20 years
- that person then decides to undergo hormone replacement therapy (HRT) for several years
- Once the hormonal profile stabilizes to resemble that of a typical female, are there any physiological reasons why that person should not compete in a women's weightlifting competition?
I could imagine that the muscle fibers are already developed during puberty to a certain extent, which would make this unfair for the other competitors, since males probably develop 'better' that way.
Also there's the fact that the male hormone profile influences growth much better than the female profile, making all 'gains' prior to the HRT also an unfair advantage. Although, biological women can take steroids, so that's not a good reason.
Please note: I do see why the sexes should compete seperately and I'm not fighting that notion right now. I'm also aware of several practical reasons for not allowing this. Please refrain from answers citing those reasons.