>

I’d say it becomes fighting or no longer productive when someone decides to start making things personal. Personal attacks or jabs at the person your talking with are usually a tell tale sign that it’s no longer political discourse. 
Jabs usually mean that there’s no longer and legitimate points to share and someone is desperately grasping at straws to “win” by bullying or in a more positive light it could be a sarcastic jab showing they are surrendering.
The system we have right now in USA is fine where everything is free game except immediate directed calls to illicit activities such as violence or disorder.
Agreeable speech does not need any protections, only disagreeable speech needs it and no one should trust a government to determine what non-violent speech is acceptable.
Let the marketplace of ideas and social pressure determine what becomes mainstream or not. Force of law shouldn't be used to shut down mere ideas. >


I understand the frustration that a lot of people have with the requirement that only incitement of imminent lawless action can be prosecuted. This makes it so that someone can say things that are likely to lead to violence as long as it would only occur at an indefinite point in the future.

It's a bad rule... until you contemplate the alternative. >

I'll talk about anything with anybody.
The worst ideas are the ones that most need drubbing in the town square.  You don't want that stuff to fester in the dark, for the same reason you don't want it held unchallenged in the light.  Discourse is the mode of social progress.
Extinguishing people to quiet dissenting opinions is the action of a propagandist.  After that precedent is set, it doesn't matter how righteous the propagandist's message was, it will turn shortly to elitism and hate. >

The thing that comes to mind immediately as what I consider outside free speech tolerance is facially untrue claims to deny elections, Ala Trump and MAGAs for 2020. Even then though it can be tolerated so long as it isn't widespread enough to actually be getting officials to overturn election results. After that violence is acceptable, but unfortunate.  There are lots of stupid ideas like that, flatearthers types that so long as it remains on the fringe society can weather them without too much trouble. >

I do want to point out that the Overton Window is meant to kind of neutrally represent what's considered politically acceptable in a given society overall, not what individuals agree or disagree with. So, for example, 15 years ago opposing gay marriage was objectively acceptable and within the Overton Window, and today it is not, even though of course there were strongly pro-LGBT people back then and there are strongly anti-LGBT people now.
As for where we should draw the line of tolerable vs. intolerable political views, I think your first category would be answered very broadly by most people, and there's a pretty big jump between two and three, so I hope you don't mind if I change your categories up a little bit. It's a complicated topic, but I think I would divide things like this:
Something you disagree with. Everyday political disagreements not covered by the other categories.
Something you strongly disagree with; you would still be willing to be friends with a person with this belief. For me this would be beliefs that I consider foolish, damaging, or immoral, but still compatible with a liberal democratic society. So, for example: hardcore libertarians (whether left-wing or right-wing), principled social conservatives, democratic socialists, "defund/abolish the police" types, separatists (I'm Canadian so I'm thinking of Quebec here), and so on.
Something you vehemently disagree with; you would not want to associate with a person with this belief. For me this would be beliefs I consider totally morally unacceptable and/or hostile to our liberal democratic society. For example: openly bigoted people, revolutionary socialists, religious fundamentalists, prison abolitionists, Alex Jones-level conspiracy theorists, and so on. 
Something unforgivable that may be extinguished by censorship or by force. I would reserve this category for those who openly and explicitly seek to destroy our liberal democratic society and/or advocate violence and hatred against groups of people. Neo-Nazis, fascists, white supremacists, anarchists, "solidarity with the DPRK"-level communists, Islamists and other religious extremists, and so on.
I say "may" because while I believe the government should not hesitate to bring the hammer down if these groups pose a threat, actively hunting them down may be counterproductive and hard to balance against constitutional rights; there may be a gray area between the previous category and this one. Exactly where we draw that line of course brings us to the "paradox of tolerance" and is a whole other discussion. >


Something you disagree with, but think is a valid POV

Libertarianism, socialism and other economic ideologies, hell most things generally. I oppose gun restrictions and mass immigration but I can at least see where these people are coming from.

Something repulsive or idiotic that should be opposed strongly, but politely.

Abortion, Biden's presidency (mostly just the DNC in general), incels, the idiotic anti-semetic ideas that Jews run everything (complete crap), and health mandates.

Something unforgivable that can only be extinguished with censorship / force

I really want to say 'nothing' but neocon pro-war interventionism has killed so many innocent people in the middle east. It's completely unacceptable. >

I like to debate stuff at work with colleagues and because we worked such fucked up hours, including overnights, it was more or less accepted due to people being bored as long as people were respectful. It was about 2 years later where I had to shut shit down when a guy got so angry that I thought he was going to be this girls ass in the office. That’s my line lol >

I used to play poker for a living (not a good living, my ceiling was pretty low).  I LOVED the 2016 election.  It was a years worth of dropping grenades at the poker table then sitting back and watching people lose their minds (and money)  The dealers knew what I was up to and would give the dirtiest looks when I would toss out a "huh, this Trump guy has some interesting positions"...then just fade into the background >

Basically everything's fair game until it becomes a threat of violence or targeted harassment. That's my line. I'm fine with people having stupid opinions. >

If it is not an immediate threat, incitement to violence, libel, orbpubkic obscenity?
Then such speech deserves the full protection under the law.
It gets dicey when we are talking about quasi-monopolistic tech giants. Social media is so new and ubiquitous, a new constitutional standard ought to exist tobgivern the parameters of free speech.
A purist would say that aprivate company can censor whatever it wants. And then one could also argue that this megacorp is a monopoly and should be broken up . . . >

I can sit and discuss politics the most extreme right wing/left wing and or other one can think of.  I can sit with an extremist ANTIFA that thinks all republicans should be destroyed, literally and figuratively.  I can sit and discuss racial issues with members of the KKK, or black isrealities
Nothing anyone says is going to bring to a place of "fighting words"
We need these discussions.  All of them.  I fucking loathe political censorship.  I loathe medical censorship. If someone wants to spout off about how vaccines are going to kill everyone. I'm down for a discussion.
I want their words platformed, so that I can address and combat them on the same platform.
Progress and change is done through conversation, not silencing opposing opinions. >

As a public school teacher with progressive views, who grew up in a poor blue collar neighborhood, I have long walked a line between my own political views and those of the lifelong friends and family. 
I usually took the ‘let it slide’ approach. But when the political right popularized the narrative that I’m a pedophile because I’ve spent almost three decades of my life working in public schools, that was my last straw. 
I didn’t fight, because it was not worth it. But that narrative, passed along in meme form, was the thing that moved me to action. And that action was to move on without these people in my life. 
So yeah, that’s my line, call me a pedo because I’ve taught in large urban high schools for 28 years. We won’t fight, but our shared history ends and, in my mind and heart, I will consider you as dead to me. >


Something repulsive or idiotic that should be opposed strongly, but politely

Misguided sexism, racism, bigotry. ex: People that have fallen into a trap like listening to the BS that Jordan Peterson spews or someone that's repeating Fox News Talking Head Bullshit

Something unforgivable that can only be extinguished with censorship / force

Outward and unapologetic sexism, racism, or bigotry. Even in this category there's scale of measured response. As the speech slides toward inciting violence the response needs to be firmer. >

Thanks for your insights!  Are there political positions you consider incorrect, but you can see the validity? >

Most political positions can be "valid". What's important is context.
Policies that work in rural Kentucky where your closest neighbor is 20 miles away may not work in urban centers where the only thing separating you from your neighbors is a wall made of paper.
As far as positions that are incorrect.. people that view abortion as murder are incorrect. >

1) sports in category one
2) American policing for category 2
3) poor education, miseducation religious indoctrination, oligarchism, socialism, communism, capitalism in category 3