A small minority didn’t like the school. Dumbledore’s followers would lose control over the children, if they were taught by professionals. Voldemort’s followers hated the squibs, who were going to teach their children, but they couldn’t protest, because the squibs were better educated in dealing with magical children better than witches and wizards with masteries to their annoyance. They swore to make Lucius Malfoy pay for his betrayal against their Lord.