Just to clear one thing up: while it's true as noted previously that the Argentines are quite zenophobic (I much prefer that word to "racist," because here it's broadly aimed at "anyone who's not like us," rather that a widespread dislike of any particular ethnicity), as far as I've ever seen in over 40 years, there's no targeted discrimination against black Americans, or black Anyones, for that matter.
Various people commented on the prejudice shown toward recent immigrants from Bolivia, Peru, etc, but that's normal anywhere where immigration happens from poorer places. Lamentable, but predictable. So what keeps Argentines from showing zenophobia toward black folks is that so few have wandered this far south. I'm not the best mind to opine on this subject - those who live here full-time are better informed - but for what it's worth I've never seen that particular type of bigotry.
Absolutely -- they can be brutal towards anyone who's "new", and part of that is because people from poorer countries have been immigrating here in recent years, and they feel they're poor enough already. However the qualification has nothing to do with being "white". If you're American I think you get a pass for just about everything here, except you will be personally blamed for George W Bush and the failed war in Iraq, because that's how they view things. These are over educated and extremely intellectual people who realize they are stuck at the ass end of the world and have no control over anything, so they take to art and cultural criticism the way tadpoles take to water. That said, I don't think they have any fixed ideas about skin color or race the way people do in America or Australia (or Thailand, for that matter -- those famous Buddhists who secretly think if you're Farang you're a barbarian piece of **** who's only good for stealing from). They have very little experience with other races, although they themselves are a mix. Buenos Aires is one of the most cosmopolitan and multi-cultural cities on the planet, My grandparents immigrated here from Europe in the early 1900s and spoke no Spanish before they arrived, and that is the story of most Porteños. (The fact that they moved on to the Bronx is only half an indictment, and in my opinion was a mistake).
The non-judgmental attitude of Argentines can be proven, versus Americans. The first two questions I get asked in America (although I was born there and speak with a native California accent) are: Where are you from? And: Where are you really
from? The third question is usually "What do you do [for a living]?" If I say "I'm American" they keep pressing. This is what some people call a 'micro-agression' in America now, but it's always been that way if you're olive-skinned and Mediterranean.
Argentines will ask where you're from but will accept America as the answer. They will never ever ask what you do for a living or what your ancestry is, unless you get to know them very well. It's almost like those two questions are just below them. And part of it is the immigrant culture and the do-your-own-thing attitude. I love this country for that, above all: I think they really do judge you here by your character. They don't care how much money you make or what your ethnic background is. If you are a cool person to hang out with you will be loved from the first day you get here.