Remembering to look for and ignore folks with that telltale indicator has made the fediverse so much more enjoyable.
Their point isn't that Lemmy.ml is a Nazi bar, but that leftists should behave like the so-called "Nazis" at Lemmy.ml. We are communists, not Nazis, and are diametrically opposed to fascism.
As for why not Lemmy.world, it comes with the majority of Marxists pre-censored for you, which for me is bad.