People talk about the middle of the road as though it were unacceptable. Actually, all human problems, excepting morals, come into the gray areas. Things are not all black and white. There have to be compromises. The middle of the road is all of the usable surface. The extremes, right and left, are in the gutters.

Dwight David Eisenhower (1890-1969) American general, US President (1953-61)

Note (Nov 1963)
    (Source)

The earliest reference I could find was second-hand, in William Safire, The New Language of Politics, "middle of the road" (1968) (later published as Safire's Political Dictionary, and including the entry through the 2008 edition).