The whole reason Facebook has any enforceable standards as a community is because of that policy. The community standards uphold themselves because there are be real-life social consequences for saying something hateful / sexually harassing somebody / posting pornography - the list goes on. Having to use your real name on Facebook is what keeps you accountable. If you want to see Facebook turn into a sewer, get rid of the real names policy. Witness 4Chan and YouTube comments.
They should make exceptions for certain cases, such as when someone is avoiding harassment, or has changed names due to being transgender, or lives under an authoritarian regime. But they can and should do so on a case-by-case basis.