Well, I personally don't think they ought to be crewing with the men at ALL... and the pregnancy issue is part of why.
If I were in, I would not have a problem with such a policy.
you don't get a choice bout the anthrax vaccine, EITHER in the service.
Contracting antrax is not against military rules as far as I know. So you're not vacinating against something that would get people kicked out of the miltary. Wrong analogy.