The perpetually evolving morality of the X-Men has always been one of the most fascinating aspects of the franchise. It's allowed old friends to turn against each other and has been at the core of some of Marvel's greatest tragedies. The mutant heroes have been pushed to the brink plenty of times. Even some of the franchise's classic heroes had brief stints where they became dangerous threats.
Source：https://www.cbr.com/x-men-original-villains-marvel/
