One of the features of fact-based discourse is that it tends to barely depend on which premises you start from. The two most common abstract moral systems, categorial morality and utilitarianism, are about as different as two can get; and yet in practice there is little difference between the political and economic conclusions they yield.
This suggests that assumptions are only necessary as a starting point, but can later be discarded once one knows enough facts to proceed. Of course in abstract ethical arguments assumptions are very important – Peter Singer’s animal rights arguments are very closely wedded to his utilitarianism. But on more concrete political, social, and economic questions, arguments tend to be settled on empirical facts.
The only time an abstract model ever has political relevance is in the form of theory. But a theory is not an assumption, but rather a hypothesis that passes many testable predictions. Social scientific theories have a nasty tendency to be ridden with exceptions and special cases, but the serious ones are empirical enough to stand on the facts rather than on any moral premise.