What I mean is that there are women who have had hysterectomies, are too young, or are post menopausal, and men who have had vasectomies or are infertile for other reasons, who cannot become or make women pregnant respectively.
If sex segregation was strictly about ability to become or make people pregnant their place in this analysis would be uncertain.
Reasonably thinking what someone can or can't do doesn't cut it, either. Who is doing the reasonable thinking? That is a subjective criterion and open to interpretation.
A class based set up is what we have and is acceptable and accepted. It should be obeyed regardless of fecundity, perceived or actual.
I know we don't disagree on who should use which sex-segregated service. The justification for sex segregation is because society (most women, and many men) demand it, and it's reasonable to have it for reasons of propriety and dignity as well as safety. Even if there were no risk of rape and pregnancy - it would still be correct and proper for women to demand not to be made to undress in the presence of men.