I think a location-based policy at the time of posting is sensible. That's also how international law work: if I smoke a joint in Amsterdam, I am not liable for it back home. When in Rome...

I also think that the policy should apply to the poster, not to the viewers. What makes our world great is its wide range of cultures, and we should not isolate ourselves in little silos. Conversely, we should not allow a single culture to dictate to everybody else what is acceptable or not.

To be fair, I don't think any policy is necessary besides moderating and reporting illegal content. But since Facebook seems quite inclined to go the extra mile to make its platform less offensive, I think this would be a good compromise.