It is exceedingly difficult, indeed impossible, to prove that any proposition has been held by all men to be true. Records of the beliefs of all men are not extant.
If there is universal agreement, it is with reference to a very meager set of beliefs. If all men believe in the existence of a material world, the views about the nature of matter are so diverse that the common elements in this belief are exceedingly vague.
Precisely in the most important matters, such as the meaning of life, the right social and economic relations, the nature and being of God, there is the most striking difference of opinion among men.
Even if there were universal agreement on certain beliefs, this would not constitute proof of those beliefs. There has been substantially universal agreement about the size and shape of the earth, and about many other matters; but later investigations have shown these beliefs to be false. The consensus genitium has to yield to the decision of a higher court. What every one once held to be true and necessary is now seen to be false and impossible. “Common sense” changes from age to age, and is itself largely the deposit left by the thought of scientists and philosophers.
Not only does the consensus suffer from the defects mentioned, but also it contains no principle for their improvement. If universal agreement be the criterion of truth, and people agree universally on some error, there would appear to be no way of deliverance from that error, so long as one trusts agreement as criterion.
We can draw only one conclusion from the evidence: namely, that widespread and even universal agreement among men is no a criterion of truth. What is universally believed (if there be anything of the sort) may well enough be true; but it is not known to be true on account of its being universally believed. It is pleasant to agree with our fellow-men; but this pleasure does not exempt us from the duty of asking whether the points on which we agree are really true.
(Brightman, Introduction to Philosophy, 40-41)