None. When science hasn't fully resolved a question based on the evidence, none of the competing theories should be used as a basis for public policy.
Bogus. Science is not about "fully resolving" but about "models that work". Yes you could back the "wrong" scientifc theory when making policy, but in most cases they will differ only in corner cases. And even better, you can choose a response that addresses the problem, no matter which theory is correct. Even if global warming today was mainly caused by volcanoes, would it make sense to pump out even more CO2?
However, if there's a debate like there is in the US with climate change, with opinions 180 degrees the opposite, you can be sure that one side is only spouting complete bollocks and propaganda. Especially when you notice that one side has most of the scientists on its side, and the other mostly politicians.