The report I heard on the radio the other day was that there are currently 11,000 known transgenders in the military, currently.
The military should be a slice of society at large, why should disproportionate numbers of a particular gender, race or <?> serve, and sacrifice for their country?
I don't think anyone is saying any particular type of person 'should' serve, just that given the general 'climate' in the military, we were feeling like a transgendered person would probably be walking into a potentially 'dangerous' environment.