It really depends. If someone is boosting as a new player to skip straight into the latest content, then they're only harming their own experience and enjoyment of the game more than anybody else's. However, if someone is boosting an alt character or simply just extra jobs then it's entirely fine. Ultimately buying a boost isn't the sign of a bad player but rather their interaction with the systems. I'd never recommend boosting/skipping the story as a new player but given that levelling additional jobs is incredibly boring, boost any job boosts that you can afford.
