I agree . . . I wasn't suggesting they are aggressive, only that I think their primary motivation in life is to eat . . . if an oscar see a bite-size fish, it will just unthinkingly try to eat it
unfortunately, it is what killed my oscar, when he basically inhaled a 4" catfish and then died from what I assume were internal injuries from the spines
this is not limited to oscars, either; I once came home to find my 5" green terror swimming around the tank with a half of a 2" white cory sticking out of his mouth . . . the cory was too big to swallow, and because of the spines he couldn't spit it out.
amazingly, once I caught him I was able to extract the cory and both fish survived (!)