The problem with your summary of the centrist objection is that it's false. The Overton window isn't narrowing -- it's expanding. Look at the last presidential elections. You had Bernie Sanders expressing socialist ideas and opposition to the 1%. Expressing those ideas used to be political suicide, but not anymore. At the same time Trump expanded the Overton window enormously to the right. Look at the political discourse in its totality and compare that to the discourse from just 5 years ago. Voices in the far right and far left are louder than they have been for at least a generation. How is this compatible with claims about a narrowing Overton window? It's patently absurd.

As for your remark about calmly states ideas: hate speech laws exist for a reason in most of the world. The United States is the exception in its free speech absolutism. A lot more harm can be done by calm speech than by a baseball bat, and free speech (like any other freedom) can be used to infringe on other people's rights. I value free speech but I don't value it over everything else, and I don't think State suppression of free speech is meaningfully different from the many other ways in which speech can be suppressed.

Bernie Sanders is no socialist, he’s basically a mainstream New Deal Democrat. His positions would not have surprised President Eisenhower, who said, in fact, that anyone who does not accept New Deal programs doesn’t belong in the American political system. That’s now considered very radical.

->https://www.csmonitor.com/USA/Politics/2015/1115/Was-Eisenho...

Trump for me wasn't that different to any of the other Republican candidates, they all don't believe in global warming and have pretty much the same agenda. He just didn't dress things up and speak smoothly, like most politicians, but says it as it is.

I didn't say he was a socialist, I said he expressed socialist ideas. For example his calls for universal healthcare and free college.

As for Trump, the discussion was specifically about what people can _say_. Trump said things other politicians didn't dare say, and by doing so he made a big impact on the political discourse. As for his agenda, in a country of 325 million even small differences between republican candidates are really significant.

"... A lot more harm can be done by calm speech than by a baseball bat"

Then it should be easy for you to supply even one example where calm speech caused a grievous head injury.

"...and free speech (like any other freedom) can be used to infringe on other people's rights"

I cannot imagine a single right infringed by someone else's free speech. Again, perhaps you can supply an example?

Kids driven to suicide because of verbal bullying for example. Or religious leaders who call upon their flock to engage in horrific violence against the other.

Indeed. I would argue those examples are not protected "free speech", since their intent is to cause imminent harm.

But point taken. I did misspeak when I said "Calmly stated ideas". I meant, specifically, any idea that is not intended to cause imminent harm. Imminent being the operative word, there. So, to my mind, "I think minorities should be turned into lampshades." is reprehensible and worthy of social sanction, but should not be suppressed. "You should kill yourself!" to a suicidal person is dangerous and potentially criminal.

Let's turn it around:

Imagine someone expresses a racist idea, and then the universe splits in two.

In one universe, the person gets a punch in the nose and their books are burned.

In the other universe, a centrist says, "that idea is reprehensible, and here's where you have failed..." and then outlines ethical, philosophical and scientific objections to the racist idea. There is a calm discussion.

In which universe is the racist more likely to consume an underground press of unchallenged racist ideas? In which universe is the racist more likely to change their mind? Which universe is more dangerous, more likely to lead to violence?

From a centrist point of view, the suppression of stupid ideas is more likely to be dangerous, than having them out in the open.

We don't have to take your hypothetical as a hypothetical. After WW2 Germany banned books espousing Nazi ideology, and punished similar speech because they learned first-hand what happens when you let that ideology roam free. And free speech didn't die. Germany today is one of the freest countries in the world.

The "banning" of media that espouses Nazi ideology is actually very limited in Germany. Hitler's "Mein Kampf", for instance, is not actually banned.

Germany may be "one of the freest" countries, but they too now have far-right parties in their parliament and there have been hundreds of attacks (assaults, firebombings) on refugees.

Also, Neo-Nazi ideology is still popular in the East, despite all the efforts of the socialist government against it. If people are shoved an ideology down their throats, the alternatives suddenly look much more attractive. I'm firmly convinced that it is the left that got Trump elected, not the right.

I think the Overton window might very well be expanding on a society scale, but that doesn't preclude it from narrowing on 'community scale'.

Anecdotally I do get the impression that engaging with others about politics ('community scale') is much more explosive these days, on both 'sides' of various issues. I get the same impression when I think about the publications that often come up in conversations. It's like two parallel universes while I know for a fact that not too long ago reading habits included much more 'mixed' publications (also generally of lower quality, but I'd say that's not entirely relevant to the overton window 'issue')

What can and what cannot be said is in constant flux. For every newly introduced taboo other taboos go away. It's conceivable that the Overton window narrows on 'community scale', but I don't see any evidence for that. In some communities the Overton window is shifted massively in one direction, but not at the expense of width.