Left/right scale is universal. You can't go out and say "Bernie is an extreme leftist" because he's a politician in the United States. ... Bernie leaning more to the left than Hillary does doesn't make him "extreme left".
OK, so let's accept for the sake of argument that Bernie is not "extreme left" as you understand it -- what is, then? What does "left" even mean? In the U.S., it is thought to equate to being "liberal" -- but true liberals (as opposed to the political label, "liberal") believe in freedom, while many "left"-ist causes seem to devalue freedom considerably.
Take, for example, the Shining Path. They are communists, so presumably they'd be considered leftist. But they aren't "liberal" at all! They set up a violent dictatorship. So, are they really "left"? "Extreme," certainly, but not exactly paragons of freedom. I use them as an example, not to start a debate about that one group in particular, but as a reference point only. It's just the first one that came to mind as an example of what one might call "extreme left" -- even though it circled around to become something the opposite of what I consider to be liberal.
For a long time, the American ethos was that its citizens valued liberty and freedom above all else. "Give me liberty or give me death," that sort of thing. Based on the political choices Americans have been making for the past decade or more, I'm not so sure that's still true. On college campuses, free speech is often under siege. But the gun debate is a pure example of that ethos, at least among some citizens: it's not that Americans love guns (though that's part of it), it's that Americans love the freedom they have to own guns.
As an aside: Do kids in school still study Orwell? Ayn Rand? As for the latter, it's become fashionable to discredit her philosophy, but I think the bigger problem is that it has been coopted by the power mongers whom she actually reviled as an excuse to aggrandize themselves and exploit others. (She would have respected Elon Musk -- she likely would not have respected most bankers, no matter how wealthy.) Still, regardless of your views on her, I assume Orwell is still highly respected by pretty much everyone, right? (If not, then we're all fucked.) Orwell, at least, should be required reading for teenagers and/or college students.