As for Argentina, read up about President Christina Fernandez de Kirchner, inflation, and the recent murder of a prosecutor about to disclose an Iran/government connection concerning the Jewish Center slaughter (around 80 Jews killed) back in the 1990s.
As for Brazil, I know women who will not go around Rio without a male escort as the petty theft is flagrant.
There are “safe” places, relatively speaking, everywhere you go in the world. You will enjoy a visit to both places, but living there?
Just to expand a bit...to give a practical example of what others have said:
On a day tour of Rio we went to a national park very close to the city called Tajuca National Park.Rio is a very hilly area and Tajuca was on a pretty steep hill.As we were climbing the hill our guide directed our attention to a nearby hillside on which one could plainly see many,many small ramshackle buildings basically strewn all of that hillside.The guide said it was a "favela" which in Portuguese (or Brazilian) means "slum".She said that that favela was *so* violent and lawless that the Brazilian *Army* doesn't attempt to enter it *in daylight*.
I could go on...stories of the 3rd World poverty I saw in more rural areas...poverty almost equaling the poverty I saw in East Africa among other things.