Thread:Rib14430168/@comment-4048025-20160318001031

I'd actually argue that Argus Filch gets to stay because in the fifth book he works for Dolores Umbridge as her enforcer. Unlike the Hogwarts staff, he is loyal to Umbridge because she allows him to torture misbehaving students like whipping them. Filch admits that Umbridge running the school was the best thing to happen in Hogwarts.

Even before, he is sadistic and domineering to the students and at one point begged Dumbledore to let him chain students to the ceiling for misbehaving. 