I don't know if that many leftists really accept England's claim, I think some are just dummies who have to react reflexively to absolutely everything and see Milei and think Argentinians are just twats. Also, the attempt by Argentina to take the Falklands/Malvinas in the '80s was done by a US-backed right-wing puppet tyrant, which lends a bit of irony to it. Even so, there's no reason that the British need to control islands 300 miles off the coast of Argentina. It's understandable that Argentina would contest British control of islands which are far closer to Argentina than they are to Britain. I think the only good argument, offhand, for British control of those islands is the small (non-military) British population, who have been there for a very long time - under the right circumstances, they could just be integrated into Argentinean society as a small English-speaking group who live on those islands, and it shouldn't
have to be a problem. Of course, the British probably wouldn't give it up without a war, which would complicate that.
As an aside, I was checking Wikipedia to be sure that I correctly remembered how long the British had controlled those islands, and there's some really embarrassing stuff in this article:
https://en.wikipedia.org/wiki/Falkland_Islands_sovereignty_disputeParticularly that second paragraph:
"While Argentina claims a right to colonise the territory for economic gain, Britain has supported the right of self-determination of Falkland islanders. Today, Falkland Islanders overwhelmingly prefer to remain British. Following the British victory in the Falklands War, they were granted full British citizenship under the British Nationality (Falkland Islands) Act 1983."Gee, I wonder what side the person who wrote these (unsourced) sentences is on!
Actually, the source for the sentence after those two is just the "Falklands Government" website, so perhaps those sentences are citing them as well (I haven't checked). Anyway, it's very badly written and someone could come away getting the wrong impression from that.