No-one's forcing you to use Quora, Quora's goal is to maintain high-quality and one of the strategies that they're using to do that is require people use their real name. It's a perfectly legitimate strategy.
Asserting that something is true doesn't make it so. I can say that you look like a ham sandwich but that doesn't mean you look like a ham sandwich. There are a number of reasons that it isn't a legitimate strategy. This story illustrates a few of them, namely that false positives and false negatives are hard to detect, and that alone is reason enough to reject the idea.
Perhaps it is useful to examine the reason for identifying people. If it is, as you say, to maintain high quality, I would ask upon what causal basis that that conclusion rests; I submit StackOverflow and HN as examples of entities that show real names not to be a requirement for high quality discourse.
