Contraceptives are devices that prevent the humanity virus from replicating. During the act of sex if a sperm meets with an egg that a woman just laid, then like Pinocchio it may transform into a real life human being, which requires endless amounts of money spent on it, absorbs all your time and energy until you go insane, and gives you a +2 to passing pity checks. To prevent this 'contraceptive devices' have been formed.