A couple points towards the end I really don't agree with-
'And what is perceived as a sexual signal won't be the same everywhere. So those map on to norms.''
This is about single sex spaces. A major reason for women and girls to have them in certain circs is because of the fact that there are a good amount of creepy/ pervy/ predatory men about and most are interested in women and girls.
Sexual signals? Dodgy men aren't interested in 'signals'. Although plenty like to think that eg a schoolgirl with a rolled up skirt is loudly broadcasting come and get me, to any and all men in the area...
'As long as women and men are together there's always the possibility of sexual frisson. '
This is about single sex spaces. To make the point- 14 yo girl getting changed for swimming in a mixed sex area and all other occupants are male. Range of ages. I imagine there would be a certain amount of sexual 'frisson' but in a specific way...
Additionally see post about Finland. Home sauna with family. Sisters uncles grandma in laws etc. Mixed nudity does not inevitably = sexual 'frisson'.
'It's inconvenient to those who want us to have a sort of sexless civil society, but it's the truth whether we like it or not. '
Who wants that? People in the UK have plenty of sex! There are plenty of ways to pull without going to s place with naked men and taking all your clothes off 
'There are ways to keep that somewhat under wrap through social norms too. But when people are doing things like undressing in a society where nudity is more private, the only way to totally desexualise that is to have sex segregation.'
Hmmm. Just thinking. Plenty gay clubs (or used to be) where it was pretty... Full on. Hardly dressed/ naked. Sex acts just around the place etc.
Surely it's not the nudity itself but the context?
And the fact is male behaviour like voyeurism, indecent exposure, and so on. It's one sided isn't it. I can't imagine many women would put a camera in a bog to get footage of men having a shit. Because they find that sexually exciting.
This equation is not equal.
Single sex spaces protect women and girls. It can be argued back and forth about the cultural stuff etc.
In the end though. Globally women and girls are the target of iffy/ awful sex related behaviour. So. We need our spaces in certain circs.