How would we go about getting people on the opposite sides of a political argument to agree on what is a "valid fact"?

It's not completely impossible...it's just highly improbable.

The routine most people go through regarding "facts" is this: they look up as many so-called "facts" as they can find that seem to support their chosen argument. They then bombard the opposition with those and ONLY those "facts", and they disregard all others.

That is how people deal with "valid facts".

Add to that that most of the so-called "valid facts" they have acquired have come from some quote from some person or organization which ITSELF has an agenda to push...therefore the "facts" may not be so factual after all...and the whole thing becomes more ridiculous than ever.

It's laughable. It's ludicrous.

And so are the endless demands for one's opponent to provide "valid facts" made by various pontificating, grandstanding people here who are merely intent on wasting someone else's time if they possibly can, for the sake of their raging little tormented ego that MUST always be RIGHT!!!

FUCK your rightness! You aren't always right, you're never going to be always right, you're never going to have all the facts...or even half of them...you're never going to be able to sort out the propaganda from the truth without making errors here and there, and you're never going to be anything more than a vain, empty noise bellowing to an online audience that frankly doesn't give a damn.

But it will keep your idle mind busy...right? And you'll FEEL right. That's enough for most idle minds.