I’ve changed my mind - I just remembered The ‘Zizians’ cult. They are absolutely the strangest group I’ve ever heard about.

https://youtu.be/9mJAerUL-7w

I’ve always found puritanical groups quite interesting. They seem to evolve out of any subculture be it religious or not. Take the ‘straight edge’ culture, a group of hardcore punk kids who rebelled against the excesses of the punk underground and swear an oath against drinking, drugs and casual sex.

On the religious front you have groups like the shakers. An offshoot of the quakers whose utopian vision prohibited all sex. As a consequence the movement all but died out as they couldn’t reproduce to create new members!