This idea just struck me reading your post, but I think it's something novel. I've read a lot of responses here, and yours encapsulates the argument that speech is subordinate to tolerance better than most. As someone whose immediate family are the only survivors of mass genocide, I'm keenly aware of the dangers of giving intolerance a platform to poison innocent minds, or of tolerating it at all. But not tolerating it, to me, means taking the time to address it rather than attempting to silence it by another act that could be portrayed as intolerant and thus give ammunition to the enemy. So I think it's succinct to say I look at the Overton Window concept like this: Anyone who wants control will try to put the window of debate where they want it, and narrow it as much as possible. The solution is not to move the window but to stand by the value of widening the window and keeping it as wide as possible. The fact that it has shifted in directions some agree with and others disagree with is useless as an argument for restricting or expanding it. Where it is wide and debate flows freely, there will be more tolerance. Where it's narrow - wherever dissenting opinion, even intolerant opinion - is treated as beyond the pale, eventually your own opinion will be treated as beyond the pale, and no one will be left to speak for you. My grandparents were communists and their family was murdered in the Holocaust. To me the primary lesson of the 20th century was that all ideology is a source of horrific torture and murder. Only by absolutely widening that window of speech as much as possible can individuals hope to fight the excesses of whichever ideology happens to be in the middle of the window at the present moment. And living through several fascist-leaning American administrations has made me realize just how temporary the current leftness of that window is, so I really shake my head when I see people of the left attempting to narrow it. I hope that makes sense programmatically, as an algorithm, if not emotionally.

Edit - because I'm just formulating this. I'd say there's no place the Overton Window can be which is tolerant. Some centers maybe more than others, but actual tolerance only exists where it is wide, and surely wherever it is narrow it will end with suppression of valid dissent.