You have said that you would never share with a stranger of either sex which is your choice but you have to realise it is extreme. Young people can and do travel around, loads of the time, all over the place. I certainly did when I was young, and my friends too!
Straw man. The thread is about the miniscule sleeper cabins on the Caledonian sleeper- which almost nobody wants to share with a stranger regardless of that person's sex - nothing "extreme" about it.
And generally even young people are sharing with a group they know or are in a large group. There will be very few situations where a traveller is sharing a space the size of a broom cupboard with one other unknown person.
The thread then degenerated into all sorts of scenarios, including one which cannot ever happen, of trans or would be trans threatening women.