In science communication, why does the idea of a public deficit always return?

For centuries, science communication has been widely perceived, irrespective of context, as a didactic enterprise. That understanding does not accommodate a political category of science communication, featuring citizens on an equal footing - some of them scientists - who share responsibility for public affairs and represent different points of view and ways of reasoning. That may harm, at the same time and for the same reasons, democratic knowledge societies as political entities and science as a body of knowledge and rational methodology. Scientists are discursively excluded from the public. The public is perceived in terms of knowledge deficiency. The latter perception has survived decades of critique, accompanied by attempts, along an everyman-as-scientist logic, to include all citizens in the scientific endeavour. But why should all be scientists? With respect to practical-political issues - as distinct from technical-scientific ones - the acknowledgement of the citizenship of scientists seems more relevant. Only, this would challenge the widespread understanding of science as an all-purpose problem solver and the consequent ideas of politics.