The original post wasn't about using someone's judgement on an issue as a litmus test. It was about the peculiar fact that you can use someone's judgement on an issue as a test of their rationality without knowing anything about the issue, if they're expressing a non-tribal opinion.

OP said: If x is a member of X, and opinion(X) = B, and opinion(x) = not(B), this indicates x is at least an independent thinker, regardless of the truth of B.

So, if you find someone who thinks that Communist economies did no worse than capitalist ones, that person is an independent thinker. But since there are very few such people here, that can't be what you mean when you say you plan to use it as a litmus test.