The Cathars/gnostics believed the material world was evil. And it is. Especially when most churches are so hypocritical and easily corrupted. If there was a Jesus the Christian right corrupted everything he stood for. Procreation was a sin to the Cathars. Therefore if you had heterosexual sex and brought another person into this world and subjected them to this evil, that was a big sin. The cathars were wiped out by the Catholic church because in the 11th century they were more popular to the peasant class than the church was. Ultimately the cathars believed this world was created by a being that is not pure and did not have good intentions.