theological conflicts

yet again I trip across a snarky tweet about a distinguished scientist using comic sans or some other whimsical and easily read on a screen unprofessional and unserious design choice in a presentation these theological wars are becoming as bad as PC/Mac or emacs/vi flame wars of yore anyone care to summarise, rationally, and briefly, why serif or sans matters? Please avoid references to unrepeatable badly controlled A/B studies, and opinion polls of helvetica-phobic graphics designers.