First, sorry to rehash this old canard.
Second, I'm aware this topic has been addressed here: Origin of myth about the hole in the sheet?
However, that addresses R' Yose ben Chalafta's behaviour, and I've since wondered if the 'handbreadth' story of Rabbi Eliezer ben Horkanos can also be considered to have contributed more to the claims due to the 'handbreadth' terminology, such as Question 11.2.2 here: http://www.faqs.org/faqs/judaism/FAQ/05-Worship/
This seems backed up by Shulem Deen's memoir - https://images.shulcloud.com/13691/uploads/MaritalIntimacyZoomExhibit2-EliezerKaroandGer.pdf
Plus some new accounts specifically about the Ger/Gur community have come to light from Sarah Einfeld (although it mentions that it is 'probably practiced by no more than a small minority'): https://www.tabletmag.com/sections/arts-letters/articles/the-kedushah-crisis https://www.jstor.org/stable/24709805
It also seems more likely than 'gentiles saw tallit katan drying and thought they were sex sheets' (or at least seems like it would have added to it).
Can anyone confirm if the 'handbreadth' recommendation is indeed taken seriously/literally by any Hasidim, despite most authorities promoting nakedness and 'closeness of flesh' for sex? There are some groups I definitely wouldn't put it past, including cultic offshoots like Lev Tahor.
I suppose it might also apply solely to the actual intercourse and not to foreplay, much like the no-light/blanket rule... which might also have contributed.
I understand why this kind of thing is not talked about much, of course.
I just always found the 'tallit katan mistaken' reasoning unsatisfactory, and combined with the articles above, plus reading Naomi Ragen's work, I found the whole concept a bit too likely to simply brush aside as a myth, as most do - Especially when they only seem to discuss the Ketuvot 48a as a catch-all and not cases like Eliezer ben Horkanos.
– ANH Apr 11 '23 at 01:17