Beware of Futurism

Encountered this Kenneth Clark quote at Terry Teachout's excellent arts blog.

 “Sweeping, confident articles on the future seem to me, intellectually, the most disreputable of all forms of public utterance.”

Might we also say the same about sweeping proclamations about the past? Is the past as unknowable as the future? Reputable historians do their best, but so much of experience must remain out of reach. Heck, that's true of the present, too.