Haven't read the whole thread, it's long. But the thought unfolding in my mind on reading this is how my own personal attitudes to it have changed, mainly spanning the last decade.
I have no hang-ups about nudity whatsoever. I don't view the human body as in any way disgusting or taboo. But there's a normalizing of fetishized behaviour of late in which safeguarding boundaries are being persistently eroded. It doesn't take much of a leap to work out where this will lead.
Drag-queen storytime in libraries aimed at children, furries attending pride marches and protests, males encroaching into spaces where females are vulnerable, AGP, some problematic policies within and surrounding schools (man dressed as schoolgirl hanging around at leaving time and nobody turned a hair or did a thing about it). The issue is the unwilling participation of bystanders in those fetishes (it's others' discomfort that is part of the kick). As for MAPs on Twitter, this is a frightening attempt to legitimize what is usually seen as the most dangerous taboo in our society.
Naturism is inherently unsexual from my understanding, but naturists by and large behave within set boundaries. And like the fetishes outlined above, this act erodes those boundaries. If it's not OK for the naked rambler, why is it permissible for them?
About 7-10 years ago this wouldn't have bothered me unduly. Now, with an added insight made inevitable by the recent assault on women's and children's rights, it does.