I agree with this quote in that there is only one truth. However, I do not agree that humans ever have known or will know that truth. As kumagai said, every human interprets things in their own way so you asserting that any single human perception of truth is more truthful than another better have some good evidence to back it up. Widely accepted perceptions of reality often change to make room for more accurate ones and clinging on to the old ways simply for tradition is counterproductive. A few good examples are Newtonian vs quantum and relativistic physics, feudalism vs capitalism vs communism, and (the subject I believe this quote is referring to) US/Western history, which has been incredibly propagandized to paint its authors in a much more favorable light than "objective" truth would.