The one universal truth is that nobody agrees. Every single person on this Earth will have a different "truth," and not everyone will agree with someone else's idea. Everything is debatable, no matter what it is. People will debate against the fact that everything is debatable! Every concept, every theory, every religion will have an opponent, a naysayer, a rival.
To go even deeper, the idea that nobody agrees means that everything is true and nothing is true, to a certain extant. Everyone's own personal "weltenshauung" is different from another's. As General George S. Patton said, "If great minds think alike, then somebody isn't thinking."
To me, opinion is one of the greatest human gifts, and the fact that nobody agrees is at the same time a beautiful wonder and a dangerous truth. Differences in opinion have caused some of the greatest events in history, from both ends of the moral spectrum. It is also, in itself, a paradox. If the one universal truth is that nobody agrees, is it still a truth?