A.N. — While I am not high on this whole character's family, this guy is generally regarded as the most disliked of the lot. Canonically, it's hard to argue that. I'm gonna take the pragmatic view here, to throw the guy a bone via motive.
234. Percy Weasley
Percy Weasley viewed life as a series of steps taken in order to reach a goal. Percy followed the straight and narrow path, rules-wise, but he was willing to step over his family to reach his intended destination.
Prefect was a box to check. Head Boy was a résumé builder. An entry-level Ministerial position was an expected (assumed) foot in the door. All were steps on a master plan to set society to rights.
Nowhere in Percy's calculations were the burned bridges with his parents and siblings, or Penelope Clearwater's letters slowly trailing off. It was all worth it... right?