I mean, probably >90% of people have been deeply drunk at some point of their life. So objetively and rationally speaking, a drunk photo is not a reasonable reason to reject someone from, e.g., a job. Maybe if such photos become widespread we will come to our senses in this?
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.