This question about the reliability of RationalWiki was closed as primarily opinion based. If a similar question were asked about Wikipedia, I think that question could have a definite fact-based answer. There is a wealth of published scientific literature and other things answering that question. Many of these studies created a metric to study the reliability of Wikipedia and then rigorously applied it. Reliability of Wikipedia is a broad question, but thanks to those studies, it is a question with a decent (if slightly muddy) answer.
In my view, the question about RationalWiki was closed because of a reasonable belief that the data to answer the question simply does not exist. I can imagine those same metrics used to examine RationalWiki. However, I bet that no one took the time and effort to do it.
I have been surprised in the past by the ability of Skeptics.SE writers to find data that I did not expect to exist. Is there some guideline for distinguishing between a question that probably cannot have a fact based answer and should be closed, and a question that has the good possibility of a fact based answer.