This debate seems to be heating up lately. There was just an article written (can´t remember, Argentimes maybe??) regarding a survey done on Portenos, took blood samples and did questionaires. At the mention of ¨being black¨ Portenos slammed doors. Sin embargo, in the end, samples show that a high portion of Portenos actually have African DNA. A large portion of Africans actually integrated into the Argentine society and slowely were less evident.
The myth that Africans were less able to survey disease is akin to saying they weren´t as highly developed, sounds latently racist, no?
There is probably some truth in the war theory, similar to what many countries do with minorities.
Last but not least, Julio Argentino Roca came in the 1800´s and committed widespread genocide of native Argentines and anyone else of color. Hence why we today see Argentines mainly of European decent.
I don´t think most Argentines know they are prejudiced, nor would the majority ever overtly express it. It is more built into the culture, similar to most countries (hello, Prop 8 in California). Very friendly people, just not exactly taught what prejudice is.

Cheers,
Kate