A society's standards, including moral standards, are not something that has to pass "evidence".
I find it silly that we ask to justify any and all decisions and laws a society takes with some deterministic, scientific evidence.
Do the "right to freedom" needs any evidence? In fact, there's no evidence at all for that, it's just a moral guideline. Scientifically, we could do the exact opposite.
Do we need "evidence" that black people are the same as white?
Or, (in a case where evidence tells us people are not as capable as us), do we need "evidence" to not treat the physically/mentally ill as inferior?
Do we need evidence that rape is traumatic? And what kind of evidence should that be? Maybe we should not believe it until we actually see changes in a brain scan in post-rape victims (then again, why assume those changes should be for the worst?). Surely trusting what they tell us is not enough -- personal feelings is no evidence.
Now, the case for "increased frequency of sexual violence" against women might, or might not, be quantified.
But the case for "longterm damage for children who view it at an early age" doesn't need to. Living as a society doesn't mean adhering as a robot to scientific notions and discoveries. It involves preferences, choices, and even risk. A society might prefer even a negative outcome, over what is considered healthier and better "scientifically" (E.g they might keep their customs re food , despite evidence that said food can be harmful or some other cusine is more nutricional. Or they might prefer to fight and die instead of collaborating with an invading army (which gives you the scientific benefit of being alive)).