Why do people say bullshit?

Bullshit is unavoidable whenever circumstances require someone to talk without knowing what he is talking about. Thus the production of bullshit is stimulated whenever person's obligations or opportunities to speak about some topic exceed his knowledge of the facts that are relevant to that topic. This discrepancy is common in public life, where people are frequently impelled - whether by their own propensities or by the demands of others - speak extensively about matters of which they are to some degree ignorant. Closely related instances arise from the widespread conviction that it is the responsibility of a citizen in a democracy to have opinions about everything.

--Harry G. Frankfurt