Actually, their origin is more tied to bull baiting than dog fighting (again, media hype). The fact of the matter is that they are, as a breed very human-centered, which makes them ideal "fighters" because they will not (ha) turn on the humans who get in the rings. Even so, they are not born with an innate dog-aggression (the breed as a whole). I've seen far more dog aggressive BCs and Goldens than Pits.

Even the dogs whose CURRENT job is to kill strange dogs have to be raised that way, not born that way. I'm speaking of flock guarding dogs who are purposely isolated from any dogs outside of the farm they work so that they are not "socialized" and will attack and kill any intruding dog. Exposing guarding dogs to others and socializing them will ruin them for the work they are supposed to do on a real farm.