sorry for the post and run - I was pretty tied up at work.
to those who say they don't "self-ID", they are following their personal biology. Trans women would say the same thing. It is also not "a courtesy" that we "allow them" to use the women's. It's the law.
Why don't we go for "third spaces"? If we have the money for that, we can also create nice toilets with cubicles and privacy for all, or? Also: the idea that trans women should not use women's toilets (walking back the EA2010) would likely lead to more problems for women who don't clock as "female". And would we need a fourth space for trans men?
Has anyone answered my question how we would police trans people's use of toilets? Who would check and how?
As for "social contracts" - I have used the men's when the women's was oversubscribed 
Regarding prisons: I am always really disappointed when "safety in prisons" is reduced to "no trans women", rather than to go much further and demand prison reform and far reaching social reforms to ensure the population in prisons drops. I'd like to see safe prisons for all. Violent criminals, independently from sex or gender, should not get the chance to hurt other prisoners.
But to take it back to Duffield: as far as I can see, she is propagating the notion that self-ID would somehow make life more dangerous for women and that is just wrong. It would just make life a wee bit easier for trans folk.