Obviously the current system in which individuals with ideological axes to grind can negatively impact communities where people don't go by their legal names. However, it's not obvious what the right rule should be. Of course I think you should be able to use psuedonyms, nicknames, stage names etc.. etc.. on facebook but how do you deal with facebook identity theft.
So I have Jane Mary Tyler Doe. I go create a facebook account pretending to be her and, if she isn't a huge celebrity, it wouldn't be too hard to convince a large number of people (probably anyone not already friends with the real individual) that I'm really Jane Mary Tyler Doe. I can then use that account to make her look like a racist, ruin relationships with coworkers and potential employers etc.. etc... unless my fake account can be suspended quit quickly. Alright how can facebook do this.
1) A real names policy. True, this has all the bad consequences above but it allows them to immediately suspend accounts but isn't vulnerable to serious DOS type attacks since a since credit card transaction or the like can quickly confirm someone's legal name and prevent any false impersonation accusation from ever causing another suspension. Given the low probability that someone with the same name wants to engage in the impersonation facebook has enough human hours to evaluate these rare situations in reasonable detail.
But this undermines an essential purpose of facebook. To let people present themselves online to the same people they know offline meaning stage names, nicknames etc.. etc..
2) A no impersonation rule. Alright now someone asserts the account Jennifer Doe is impersonating her. What can facebook do? If the suspend the existing account things are even worse since instead of creating a fake account someone with ill-intent asserts that the current account holder is an imposter gets their account suspended and now controls the only account representing itself to be Jennifer Doe's. Given the size of facebook they simply can't stop anyone from creating any new account with that name and the impersonator could create an account Jen Doe.
The very fact that people are allowed to use names other than their legal names means there is no good heuristic to see who is likely the deliberate imposter. After all Jennifer Doe might be the name she goes by in school but the name on her birth certificate could well be Bertha Jennifer Doe and Jennifer might not even appear on things like credit cards meaning facebook doesn't even have a good guess as to the imposter.
Also this creates the possibility of a DOS attack against any account (keep claiming it is an imposter account from accounts). If facebook eventually stops viewing such imposter accusations as real then any imposter who gets their before the real user can simply launch a bunch of accusations of imposterization at themselves until they insulate themselves against any accusation from the person they are actually impostering (after all they can be a perfectly legit Jennifer Doe account then change their picture and other details later to impersonate a target).
What they should do is basically implement a web of trust style infrastructure. Facebook can start occasionally asking people who frequently message or are listed as close friends whether the person they talked to or the person with that email address really went to school such and such. Also friend requests should include a couple of selected bits of public info (like email address and the like) which, would hopefully make impersonization more difficult.
Ultimately, however, facebook needs to have a attestation system akin to key signing. You get your close friends to attest that the person whose picture and details appear in the facebook account really controls the account. Details will be a pain in the ass but it's the only plausible way since impersonization is a matter of details like schools, pictures etc.. etc.. not real names and facebook just can't check those themselves. They can only create tools to indicate potentially untrustworthy representations.
We can force them to do this by using their real name policy against immigrants. Even my immigrant friends from places like Russia are known by significantly different names than are on their legal documents (and those are often inconsistant). Chinese immigrants often have legal names that even many close friends don't even know. If we start a campaign to force all these people to use real names both the spector of being seen as discriminatory plus the real risk to their business will change the policy damn quick.