Step 1: Justify genocide.
Step 2: Justify the invasion and conquest of nations presenting no threat to you or yours.
Step 3: Justify indoctrinating teenagers into a terrorist cell and regularly paying humans to attack them as if to kill them, to keep them scared enough to stay with you.
Step 4: Justify just being a cranky fart all the time.
With those four steps accomplished, Magneto is pretty justified.
(Or, we can be super offensive and use the Holocaust. Because like all Holocaust survivors, Magneto was forced to become a mass-murdering terrorist bully often harboring genocidal cults and terrorist cells.)