ruso or rusito in Rioplatense Spanish has somewhat of a documented history as an antisemitic slur

No, not really. Anything can be used as a slur, and anything can be used affectionately. By your rule, then Negrito is also a horrible word, yet people call each other Negri/Negro/Negrito with affection.

Luis D'Elía

If it's that kind of subhuman trash that you're going to use as a measure of Argentinians, then just about anything is a hate word. This is a guy that hates everything except for the fortune he has stolen for himself.

radical leftists here have been historically persecuted by the right, the populist left (i.e. peronism) or otherwise marginalized by society at large

The same has happened in most of the world, and actually the same happened in communist countries, until the communists took power and established a dictatorship that threatened to at the very least ostracize and sometimes outright murder any dissidents. Taking that into account, Argentina is not particularly anti-communist. I did make an exception in my original post, because of obvious things like the Triple A, but the truth is that while most people didn't want communism for Argentina, they didn't demonize it the way it was demonized elsewhere. During the Cold War, the USSR's public image in many US-friendly countries was the equivalent of ISIS now, and Communist was was Terrorist is now, just a word you can't even consider, the worst thing you could call anybody. Meanwhile, we did have socialized health care, welfare, public companies, and a bunch of other stuff that would be unthinkable in the US at the time. Communist here was never an insult outside of a few radical groups.

I can't speak of their hypothesis regarding comparative literature, though I reckon that Dostoyevsky and Arlt constitute a rather meager corpus for any such extrapolations.

You can't speak of that hypothesis, yet you outright dismiss it. Russian Realism was one of the most influential movements in Argentinian Literature, this is a well established fact, academically accepted. In the first quarter of the XX century, the Florida Group of artists was in clear opposition to the Boedo group. The Boedo Group defined the Florida Group as elitist, while defining themselves as anti-vanguard and concerned with Social issues, and their artists defined Russian Realism as their main influence. The Boedo group was one of the most important organizations of our modern literature, and counted among its members artists such as Arlt, Jauretche, Marechal, Homero Manzi, among others. Meanwhile, one of the most important members of the Florida group was Jorge Luis Borges, who often talked about the Boedo group, sometimes very seriously, but eventually acknowledging that this rivalry was partially a joke, and they didn't actually hate each other. I could talk for days about this, but I'm not going to write a dissertation on the issue here. If you have any specific questions, I'll be glad to answer them. There is also a lot of material you can study, there are countless writings by prominent academic authorities about the close ties between Russian Realism and Argentina Literature of the first half of the twentieth century.