When you choose to advocate for a particular cause, there are certain things, certain issues, certain tropes, that you find yourself having to deal with again and again. If your beat involves taking on racist tabloid pricks like Richard Littlejohn and his ilk, you will constantly be having to explain that 'some of my best friends are black people' is not a valid defence. When you deal with bad science, you will have to explain the difference between correlation and causation until you're blue in the face. Set yourself against the lies of lying liars like the Taxpayers' Alliance or Migrationwatch, and you'll develop a near-supernatural ability to skewer bad sets of statistics.
If you deal with trans issues, the thing which crops up as often as the Riddler in the 60s Batman series - and is about 200 times as irritating - is the toilet thing. Every now and again, some right-wing, kyriarchal fuck decides to spread the toxic meme that allowing trans people to use the correct toilets will be a green light for any rapist to pull on an unconvincing frightwig and run wild in the ladies' loos like Molestozilla. The fact that this has never fucking happened - that there are, in fact, a number of reasons why it would actually be kind of impossible - never really bothers these people. They run with it because it allows them to trot out the old tropes about trans people being deceptive, not 'real' men or women, perverted, etc etc. It allows them to spread the fear for their own twisted advantage. It allows them to divide and conquer and, because the people they have to crawl over are some of the most vulnerable people in society, they figure they can do it with little chance of reprisal.
I set down my thoughts about all this a while ago, and now, after legal blogger Jack of Kent has ruminated on the issue - leading to some interesting and insightful comments - Natacha Kennedy has also outlined an interesting theoretical perspective on why many people obsess over this issue on her own blog, Uncommon Sense.
What it comes down to, in the end, is that, as always, it's the kyriarchy, stupid. And as Little Light points out, we have to fight the kyriarchy because, basically, the people who support it have already decided they're at war with us. And one of the ways we take on the kyriarchy and its supoorters is by explaining why the 'toilet argument' is bullshit: and we'll do it all again the next time it comes up, same bat-time, same bat-channel. C'est la guerre.