"The word "truth" itself ceases to have its old meaning. It describes no longer something to be found, with the individual conscience as the sole arbiter of whether in any particular instance the evidence (or the standing of those proclaiming it) warrants a belief; it becomes something to be laid down by authority, something which has to believed in the interest of unity of the organized effort and which may have to be altered as the exigencies of this organized effort require it."