I’m not sure this is really the right tact to take, as the people you’re arguing with don’t just believe that casual sex is harmless, but that it’s something normal people can’t live without. People who don’t engage in it (or at least don’t want to engage in it) are either “repressed” and about to burst or are odd perverts who should be viewed with suspicion. Sex isn’t something that people think a person can control. They see people claiming celibacy and chastity and ‘obviously’ they’re all secretly engaging in self pleasure because nobody can go without that regardpess of what they preach.
It’s just such a different mind set. And if people HAVE to have sex, then preaching abstinence and the risks of contraception failure or what have you is ineffective, as abstinence is “absurd” and can’t even be considered and, if everyone must be sexually active to be healthy, then casual sex with protection is “better” than casual sex without by all their metrics.
Sorry, I didn’t link you to what you wanted. But I don’t think you can make an argument on any statistics that contraception is bad, because they’re approaching the issue from such a fundamentally different position.
We have to show them that abstinence is not weird and that sex outside of marriage is wrong by other means, mostly by example and by living the good news.