I am suprised that the "T" word (terrorism) hasn't been mentioned more often as a theory today?
As much as we would like to brush this aside, I am sure that "radical groups", especially AQ etc are not considered a threat in south america, and perhaps the terrorists have realised this too and have managed to breach security in Rio?
Why are you surprised?
There has been NOTHING to suggest that this was a terrorist act. No terroist organizations have claimed responsibility. The airline was not advised of any threats to their aircraft.
Why try to stir up speculation that NONE of the (limited) available information can support? Fear-mongering is all you're doing.