Yes, pirates were freebooters and "swashbuckling" and ungoverned. However, I believe they could be quite brutal to each other, even under the guise of camaraderie. We wouldn't exactly want to liken Trainers to pirates, unless you would consider training that crass.

Pirates are also often portrayed-- and rightly so, given their history-- as antagonists. Ninjas are seen as less of a negative force.