I mean Argentina does have a horrible history of racism and ethnic cleansing, and of course we know that their current players have said and done racist things. I don't doubt that some of their fans are racist. So I'm not a particular fan of them. But most of the above things are present with many other nations, too. If it's not Argentina fans and players singing dodgy songs about French players, it's a Paraguayan politician straight up abusing Mbappe.
So I think the main reason they are particularly hated now is just because they are winning too much. That is also the source of the conspiracy theories as well, you see it across sport, especially in the modern social media age. Anytime a team starts winning a lot, people will start saying that they are being helped by the governing bodies or the refs.
This of course makes no sense, because when Argentina get knocked out (and I think they will), those same people will go back to thinking everything is legit. Make that make sense, FFS. If it is rigged then it is all rigged, including for the team that you like, not just the team that you don't like.
But of course, it's not rigged, and people deep down know this, I think. Saying that it is rigged is a coping strategy when your team or your favourite player doesn't win. Because no one wants to hear that it is rigged when their team wins.