One could also use your reasoning to claim that no statements can ever be made about the impact of economic policies, because once they're in place, we can't co

One could also use your reasoning to claim that no statements can ever be made about the impact of economic policies, because once they're in place, we can't compare with a world where they wouldn't have been adopted. Best we can do is keep a set of statistics and try to correct for multivariate bias. Doesn't mean we're navigating all of this completely blind.