People in ancient cultures were much more prone to disease and infection. While sex is fun it is, to some degree, dirty, and can lead to infections that could be highly irritating to possibly fatal. While many of the bibles guidelines on sexual practices (most of which are found in Leviticus) can seem to be directed towards condemning certain people or practices, they are mostly guidelines on how to avoid and prevent infections. An uncircumcised penis is far more prone to irritation and yeast infections. Anal sex, and sex with a menstruating woman can lead to serious yeast, or bacterial infections. Oral sex can lead to thrush, which can be deadly. In ancient societies, it was wise to keep the genital area clean. This was done by practicing what was considered safe sex for the time, which meant having penile vaginal sex only, and having it rarely.