I've personally seen wonderful birds devolve into feathered terrors because there was an incident and everyone freaked out and no one wanted to handle the bird anymore, interactions through the cage bars with me they still seemed very loving but it would've been too much of a lilability for them to let me try to handle. =(
Sadly, that is the story heard most often...
Maggie came to me as a throw away. She ended up locked in a cage unhandled for 8 years! (She's been my best buddy - and a shoulder bird - since day 4 at my house!)
Here's the deal, birds that don't get handled DON'T STAY TAME.
Attention oriented birds who get locked in cages, and don't get interacted with develop psychological scars from it... and become angry.
Life in solitary is a form of slow torture... especially for a bird that is used to being interacted with until that point!
If they get bite pressure trained... they pinch. They don't bite! It's a relatively simple thing to do, but people don't do it, or don't know to do it...
And then there's an accident, people stop handling them, and they turn on them. THE BIRD is labeled aggressive...
Actually, the bird has "betrayal issues" with you, because you were unwittingly torturing it for many years...
AND THAT is my experience with most "aggressive" macaws.
The problem with the vast majority of these "problem birds" is HUMAN!