I think that we should also bear in mind that there's a big difference between:
1) Voluntary segregation; and
2) Forced segregation.
I have no problem with the former. If women who do not care to participate in coed classes will go get training in a women's only class, I'm OK with that. If such women are more comfortable in that environment, then it's no skin off of my nose. I'd rather they got some training without men present than no training at all.
As to the latter, that's a problem. If it were "here's the women's class, and that's the only option for women," that's a proble. I will grant that from the other side of the coin, the men's perspective, if there's a women's only class, and men are not allowed to join, that's not so voluntary for the men. However, I don't think men have traditionally had a problem finding classes geared towards them.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.