In fact, there are very few subjects where reality is a matter of fact and there is an absolute truth.

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"

This. There's a point even in academic fields where you find a particular community divided by subjectivity (strings vs. quantum gravity). I think the scientific attitude of "remaining skeptical" has served us pretty well in the past. But when it comes to emotional stuff, people just have a really hard time.

You need to distinguish "remaining skeptical" from bring "willfully ignorant".

You should be skeptical of people who questions widely agreed historical facts as well.

You're right. Another thing that scares me is how we interpret history based on who wins. We've all heard the true saying "the winners write the history books".

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.