Your position is they are not extreem. Mine is that what we call left is already too extreem. However what the 'right' wants is different but mostly not in the direction I want to go.
The US Left doesn't represent a broad enough population to win most national elections; certainly not enough to pass national law. They win local elections in places like SF or Seattle that were Harris +52 (e.g. contrast with Maduro's fake election only claiming a 9 point margin) and are over-represented in Dem party donors, which influences Dem representatives.
Nevertheless, they express extreme positions. Like "people should be treated preferentially by race" or "private property should be abolished/confiscated" or "the police should be defunded" or "transwomen should be allowed to compete in women's sports categories" or "illegal immigrants should receive taxpayer-subsidized healthcare." These are like 70-30 or 80-20 issues at the national level, with Leftists on the wrong side.
Ok. I think I adequately answered that. They're a minority faction; they can't pass laws. I think you know this, and your comment suggesting a faction must pass laws in order to be extreme (bluGill's contention) was a deliberate sleight of hand.
A minority of people in the developed world would agree with your assessment that the American left is "extreme". It's mostly American "centrists" and conservatives that think so.
Again though, the original point is that left/right assumes there are extremes. All you have said is that in the rest of the world the "left" is more extreme.
If that extreme is good or not is a mostly a value judgement - there is no right or wrong answer. There are consequences to what answer you pick though.
I know you said there are consequences to which one you pick, so we partially agree. But "There is no right or wrong answer" implies all value judgements are purely subjective, that all values are purely subjective. But I think we agree this couldn't be farther from the truth - these values _govern society_ - they affect everyone around us. Choosing bad values is genuinely harmful. Having the value that slavery is okay isn't just subjective, it's harmful and evil. Maybe if you believe slavery is okay, then you might disagree, but it doesn't make you any less objectively wrong. We could get into a big long thing about how this becomes objective, but suffice to say, if people do not want to be owned, and see being owned as harmful to them... then... they are being harmed.
The thing about extremes is you can make anything so by choosing a reference point. My reference is from the centerpoint of most prosperous and educated countries, because those are most likely to be ones with good ideas to be emulated. All decision we make are based on value judgements. Obviously there's no way to know what the most sensible thing is but in absence of perfect heuristics, "what other successful countries think" seems like a good one.
It really doesn't matter what non-Americans think in this context; only Americans get to vote in American elections. (And additionally, I think you're essentially wrong that American politics is to the "right" of other developed countries in general.)