This is putting the cart ahead of the horse. What's needed is a standard by which you can say "alt right is fake" while "CNN (or insert other site that fits your world view) is real".
Even knowing this specific case is very clear to all of us, cherry picking which side is true and which one is false on ideological matters can be tricky. The line between truth and censorship is very thin.
Why don't just all of us learn to put everything in doubt? We've passed from "this is true because it's written on a book" to "this is truth because some jerk wrote it on Facebook"
You should be skeptical of people who questions widely agreed historical facts as well.
We all might have been saying things like "it's a good thing we killed all of those fucking jews, it definitely saved humanity from being tainted" without anyone flinching.
This is the kind of stuff you still hear in neo-nazi circles. But imagine -- if we all thought that.
It sure is poetic how little of a choice we have in our opinions and world views, yet how passionate we are about them. Most people reading this right now would never think themselves capable of thinking such a thing.
If things turned out differently, the accepted world-view might be that certain lineages are tainted and that they reduce the pureness of people -- it may have been punishable to even dispute this.
Anyways, perspective.