The American empire has been working hard to weaken the South American continent ever since the world lost the war. Imagine if they did nothing. South America would be USSR 2.0. The last thing they wanted was a strong, communist power below them. Not to say that I condone the atrocities of the CIA in Central and South America. Fuck no, America's crimes are unforgivable.
But I understand why they did it. I know this sounds fucked up (and possibly retarded), but I think it needed to be done. Communism was spreading too quickly in that part of the world.