They wouldn't have known that STIs spread by sex back then...
actually they did
when someone with warts gave it to someone else and they were on their genitals.. it kinda reveals how it was passed.
same with 'crabs'
when they have 'coldsores' (herpies) on their mouth but no one else eating the same diet has it then its not the food. but then finding out that person gives blowjobs to loophole the non penetrative sex clause. then they again find out its genital transmitted
also when gay roman soldiers mingled amungst many people but only had sex with particular guys. the could work out thats its not transmitted through handshakes if only the sexual partners got it
yes back then they knew about diseases and said to follow 'gods' rules to avoid diseases
when calling those who have random sex, unclean. not treating body like a temple, impure
who wil be 'smitted' by disease and death.. well thats saying in modern language. have random unprotected sex and youll get an STD
..
i know you might think that 2000 years ago people were cave dwellers
but did you know that math, writing and even alot of civilised stuff existed
not just making pyramids or colosseums but also having things like bars, hotels, barns, houses. heck they even had a census
..
now think how to implement a government rule with punishment/concequence but without having civilians riot/revolt against the government.
pretend a ghost that no one can see or touch made the rule and the 'government' are just the messengers.
and boom instant laws without the riots/revolts. cant attack what you cant see
here endeth thy history lesson