A modern notion of hard-nosed common sense is to appeal exclusively to positive facts. This is also a major basis of simplistic notions of empirical science. Serious scientific methodologies are more indirect, and quite a bit more involved.
From a broadly Kantian point of view that I think Plato and Aristotle would also endorse, all putative facts are really just assertions of facts, made by people. The validity of the corresponding assertions depends on the soundness of the reasons that lead us to believe them. Thus, regardless of whether our concern is ethical or scientific, it is always the quality of reasons that matters in assessing the validity of assertions.
The notion of a fair and objective weighing of evidence for or against an assertion presupposes that we symmetrically consider the pro and con, as Plato emphasized in his discussions of “dialectic”. But the simplistic bias for positive facts results in an inherently asymmetrical treatment any time we have to deal with incomplete information, because what putative facts we currently have in our possession is in part a matter of sheer chance.
In a fact-biased approach, if there happen to be insufficient facts in our possession to adequately support a hypothesis, the hypothesis is likely to be be dismissed out of hand as “speculation”, regardless of how inherently plausible it might otherwise be. We end up assuming something is not true merely because we cannot empirically prove it is true. This is independent of any other prejudice that may also enter into situations involving human judgment.
Once again, I want to recommend a prudent suspension or qualification of belief in cases of incomplete information, rather than active disbelief. (See also Debate on Prehistory.)
The Postmodern Peripatetic 