Some people have their (foreign) names outright banned on Facebook because they happen to be offensive in other cultures:

http://www.mirror.co.uk/news/technology-science/technology/f...

At least if the real name policy wasn't required they could go by an inoffensive alternate name... but I think it's also unfair to police real names like that.

An interesting footnote is that one of the examples in that article was a Facebook employee and the company still treated them like shit.