People should be allowed to discriminate against transgendered persons, just as people should be allowed to discriminate against schizophrenic persons.
...or anyone else for that matter. I think we'd be a lot better off if we went back to respecting property rights and the right of free association, even if it leads to "unfair" results that some people don't like.
This is why conservatives should always be wary of empowering the government to achieve social goals they desire. Eventually those powers will be used to bite you in the backside.