When the evidence is mixed on a topic, it seems natural to default to tradition.
I don't think you mean "tradition" in the usual sense here, given that the paleo diet is a (putatively) scientific reconstruction rather than a traditional practice (i.e. one handed down through generations).
I recently came out against paleo in the open thread, and realized that I probably haven't yet heard the strongest arguments in favor of a paleo diet. So, what are said arguments?
EDIT: Or more generally, why should I eat less carbohydrates and more protein / fat?