I wonder, quite seriously, how useful gender is when you're a security dude. At the library, where students aren't supposed to use each others' borrowing cards, it was sometimes useful in a very crude way, assuming you could correctly guess the card owner's gender from their name. But now we have photo IDs, just as a passport or an ID card would have a picture - surely that's about ten thousand times more useful and accurate in checking someone's identity than an M or an F. And anyway, how likely is it that someone Up To No Good would attract attention to themselves with an ID showing the "wrong" gender?