People should basically use their common sense here. A man who considers himself female but still has all the physical attributes of a man should use the male bathroom. A woman who considers herself to be male, and has gone through the necessary surgery to be a man should also use the male bathroom. Essentially, people should determine which bathroom they use upon the basis of their present body, not the one they wish they had. Obviously, the birth certificate stipulation here doesn't allow for that, so that should definitely be examined upon practical grounds.
This is shockingly progressive from you, Cassius, but my question is where do you draw the line. Most trans men haven't had the genital surgery; would you make them use the women's restroom.
Well, you know, I'm hardly an expert on the whole trans thing, to put it crudely, and I'm not really acquainted of the whole spectrum, if you will, of what being 'trans' (a broad label, as I'm sure you'll agree) entails, and I have very little idea of how gender reassignment works. Going back to the common sense comment I opened with, I'd tend to go with the view that 'if you look like a man, you should be using the male bathroom'. Obviously, masculinity and male looks are in of themselves subjective, but I can't really think of a better solution to this. I mean, public bathrooms are public places, and I wouldn't feel comfortable with a trans person who, to my eyes (given that they would be a stranger to me) was a woman, using the male toilets, and the reasons for discomfort would probably be even greater in the reverse situation. I think a system where any person can use any toilet regardless of gender would be open to all manner of problems (for instance, male pranksters, or worse, claiming to be trans so they could enter female bathrooms), so I think the best bet is simply for people to use the bathroom that they would look less out of place in.