I haven't read the original exchange in that forum, but I'm astounded that anyone would make that claim ("there is no racism in Argentina"). During my numerous visits, staying for a month or more, I was appalled by the casual racism displayed by many in Buenos Aires and in Patagonia. Even well-travelled Argentine professionals lamented that the capital was not as 'white' as it used to be and was becoming more mixed (like London, as they put it).
My apologies if this true story offends but it is illustrative. The most jaw-dropping racism I ever heard was at a dinner party of medical professionals, in a smart restaurant, who complained how much more prosperous Brazilians were becoming. Tho I speak Spanish, I didn't at first understand that when they talked about holidays in Rio and Punta del Este and complained about the 'monkeys'... that they were referring to their Brazilian counterparts