This still doesn't make any sense:
pay taxes for everyone’s health care
This was never up for debate until let's say 2003 when Conyers introduced medicare for all. Then it was up for debate in pockets of years, and it really matters specifically what you mean by who's debating in that window. Politicians or news media.
So roughly these are the open Overton windows for universal healthcare
follow international law
This was never really up for debate until 2001. The US simply just broke international law when it saw fit prior, and after.
not do extrajudicial killings/imprisonment
This is essentially the same as above. See our various policing actions in the modern era. MOVE, Japanese Internment, Mexican "Repatriation". Lynchings. Pinkertons. No real debate to be had here, America just does it and then does paperwork to justify it.
not be personally or institutionally racist
This has essentially been debated since the start of the US. So it's been "in the window". But in practice the position has always been right wing even to this day.
I would argue that the stage where a society starts to openly embrace its crimes is the one to be really worried about.
Open embrace of crimes is worrying sure, but in practice it's not practically better than doing crimes, denying you do them, and pretending you're good. Because in reality, what you can see on the left as "open embrace of criminality" on the right is seen as "being the good guys". So the open embrace may qualify as an increase in magnitude but not a change in direction. I'd love to see this actually proved out, rather than just said.
This also pretends that the causes of these shifts are not a change in material realities, but rather a change in attitudes ex nihilio. When every empire thinks its fading it does this kinda shit, because this is the kind of shit that builds and maintains empires. It's not because the "bad guys" are in charge.
A large portion of the reason that these things never came into debate until the 21st century is because the US was cruising off of the compromises made as part of reconstructing the rest of the modern world post WW2. Those compromises started being untenable in the 70's and have created these debates in the 2000's, 2010's, and 2020's solely because they are crumbling.
The most important of these debates happened behind closed doors before most of us were even born. The Overton Window shifts rightward not because it's a nerdy window function, but because it's a marble on a table long enough so that it takes the marble a century to traverse, and that table was set up a century ago to be tilted to the right. The ratchet effect is because Democrats defend the core compromises made in 1945.
This is a position you can no longer seriously hold in America in 2024. Public debate on these issues does nothing. You can look at the public attitudes towards plenty of policy positions that when polled have an overwhelming majority of support across the country but have been politically nonviable at the federal level:
We can have open debate till we're blue in the face. We can march until we wear out our shoes. The liberal tools have failed us completely in actually moving the political dial. These tools have been defeated in the modern era by experiments at the imperial periphery. I suggest you read If We Burn by Vincent Bevins.
Legitimacy is not a real discussion point in this country, it is assumed. If it were we'd constantly ask why is our democracy legitimate when the government is not actually picked by a majority of our population. Democrats in their racism are blaming Latino men. The percentage of Latino men that voted for Trump is a minuscule percentage of Latinos that can vote in this country. The overwhelming majority of Latinos didn't vote in the previous election. The president is picked by 1/5th to 1/3rd of the population eligible to vote. If you were to boil that down to a friend group you'd have a social intrigue movie in the style of Bodies Bodies Bodies.
If we liken this to the problem of consent with sexual relations, the US rules on tacit consent at best, and generally coerced sexual assault and when those don't work outright violent sexual assault. If legitimacy was a real issue the US would rule on enthusiastic consent. But it doesn't.
Parenti's lecture is meant to disabuse tankies of advocating for censorious democratic centralism of the USSR. It does not work in the context of the US because the system of control is completely different. If a country is a boiler that you need to keep from exploding, the USSR worked by creating the most armored boiler possible. The US works by having a minority or impoverished person or some other type of scapegoat put their face in front of a pressure relief valve and open it. The end result in the context of ruling a country is the same, the architects of the boiler are well insulated from its negative effects.