It's not difficult though. Just take the highest common denominator, then apply your own rules - in this case Facebook's own rules. 18+ is common in most countries, so that's a safe guideline. FB disallows porn / nudity, so, also easy enough (should be able to filter out 99% via image recognition). It's not difficult to set guidelines there, and IDK why you're trying to make it sound like it is. FB doesn't need to be tolerant or skirt on the edge in this regard. Nobody does. There is no reason why anyone would post nudity of any sorts on Facebook.