Seeming sure of who the spies are is a strong strategy -- but it's equally strong whether you're resistance or a spy. Accurate Bayesian reasoning is only a strong strategy for the resistance, since spies don't want the truth to come out. Spies want to lie either way, but it's much easier to lie in a finger-pointing contest than in a discussion of evidence and probability updating.

Using explicit Bayesian reasoning is less likely to lead your teammates into bad judgments of the kind I touched on (stemming from over/under-confidence), and it gives your teammates evidence that you are resistance.