This article takes an interesting look at the issues with Facebook's true name policy and the impact it has on activists and dissidents in repressive countries. It quite rightly talks about the fact that for most of the history of the Internet use of "screen names" was the default.
The odd thing about this debate is that there is basically no authentication of the names used. Many people assume that since most users are under true name that all of them are. It is trivial to set up a new account with a plausible name which can not be traced back to the real user.
I would hope that dissidents, activists and others at risk would take advantage of this simple capability to protect themselves. Yes, this is in violation of the terms of service, but I think it is for a much greater good.
If you choose to do this, take care with who you friend under this alias. If the social network you create matches your real one, or that of another account, it may be very easy to unmask your identity.