And I disagree with that statement too. So do various researchers on families and marriage. (I'm horrible at remembering sources, I'd have to hunt them down if you really want them.) And I'm sure there's differing conclusions among researchers since there always are. But my point is that there are legitimate oppositions to the idea that consensual sex is OK, both religion/moral and scientific.
I won't bother chasing down religious or moral objections, but please do back up your statement that there is scientific opposition to consensual sex.