The Overton window is real, but it's fairly wide open.
I could post a pro-socialism argument and get upvoted, I could post a pro-capitalism argument and get upvoted. I could criticize GMOs, or praise them. I could probably defend Trump if I'm thoughtful about it, or decry him.
Can I say "Capitalism/Socialism/GMOs/Trump is dumb" and get upvoted? No. Can I point out problems (or benefits) of them? Yes--so long as I'm not inflammatory about it.
When a post involves gender and/or race, the Overton window is quite narrow. Those appear to be the most controversial with the comments section filled with snark and polemics.
No, not really. You can't 'disagree' with pedophile politician rings any more than you can disagree with the moon landing having taken place. The one is reality, the other is not. That's what the nonsensical stands for.
It is quite interesting what people are willing to believe when individuals in power state these things with great certainty. But personally I prefer to have my fiction and real-world views separated by a healthy dose of skepticism.