This upvoted answer consists entirely of a quote from this Physics.SE answer. While I certainly don't doubt the correctness of the answer, does it meet the Skeptics requirement of providing answers with well-referenced sources?
As long as it is a primary source, and depending on the context, I don't see why not. It is one of the few ways in which we allow theoretical answers to be posted. Of course, we expect the answer to be highly upvoted and not controversial on the site of origin.
Clearly any allowed source is not automatically a good source. The correct action is to vote or flag based on the quality of the evidence, as any other answer.
In this particular case and in my opinion, the issue was that the question was theoretical and the only way to answer it was equally theoretical. Of course this meant that any answer was never going to be satisfactory to our standards. The cause of it was not the source, it was the badly posed question.