They didn't know Quicksilver had convinced Wanda to change reality, they thought it was Magneto.
This was the first time most of the X-Men were made aware Maggs was even alive, and their last experience with (what they thought was) him was Planet X, where 'he' "reshaped New York into a pretzel", murdering hundreds, and also killed Jean Grey (in a way that stuck for longer than it had any right to), so they were still thinking this was not only Magneto pulling the strings, but a version of him worse than even his worst self.
Combine that with the history they already had with the man, and the fact that NONE of the X-Men take kindly to mind control or memory alteration, and it was a pretty classic vendetta scenario.