How could there be documented evidence? It's like saying that abstinence causes STDs. The truth is that homosexuality/hedonism/promiscuity promoters are promoting evil, and in order to do so, they have to lie.
Simple.
Yes, it does sound simple to you and me. But how do they rationalize the claim that abstinence results in more cases of HIV and STDs? Any ideas? (I know a Ph.D who made this statement, and he inferred that he had read scientific evidence.)