"90 percent of people do it" is not an argument against rejecting someone for it. If I had two otherwise-identical candidates but one of them had photos of themselves online passed out in a pool of their own vomit and the other didn't, I'd pick the one who didn't. Same for other evidence of poor judgment, like a picture of them in a racist Halloween costume or comments mocking a disabled person or screenshots from an oh-so-funny thread on 8chan. If you don't want something to be part of your public image keep it private.

I'd say it's quite an argument. If 90% of people do it, it means that there is a 90% a prior probability that your other candidate has done it as well. So there is a 90% probability that you are basing your decision entirely in a non-factor. Surely there are more meaningful differences* between candidates to take into account that one that has 90% probability of not even being there at all.

To each their own, though.

*I know you said "otherwise identical", but that's not a very realistic situation and if it did happen, it would justify choosing by just any irrelevant difference, like one candidate having one day of work experience more than the other, so I don't think that says much about the importance of a criterion.

A 90 percent chance is still better than a 100 percent chance, especially when it comes to public evidence. 90 percent of people have probably said the N-word but I'm still not hiring somebody with public video of them doing it.