Warning: SPOILERS for Immortal X-Men #10If Professor Xavier and is Professor X's immense telepathic powers - and Xavier knows Magneto would wipe out humanity without a second thought.
Currently, Magneto is an ally of Xavier, as are many former X-Men villains; mutantkind united in 2019 as part of writer Jonathan Hickman's X-Men reboot. The nations of humanity collectively recognized Krakoa (except for a few nations, such as the UK) in exchange for life-altering drugs created on Krakoan soil using mutant science. Unfortunately, the island has done very little to curb humanity's hatred of mutants, especially in the aftermath of the Judgment Day event, in which the secret of mutant resurrection was revealed to the entire world.
In Immortal X-Men #10, written by Keiron Gillen with art by Lucas Werneck, the evil Mr. Sinister's plans to murder Hope are foiled when the most important mutant for resurrection is brought back to life. As Sinister is hauled into the Krakoan Pit, Xavier realizes that mutants truly are dangerous, and humans are right to fear them. "Know this with absolute certainty" Xavier muses. "If our places were switched and Eric had my gifts when he was at his absolute worst, there would be no humans left alive today...imagine if I were simply corrupt."
Magneto With Xavier's Powers Would Destroy Humanity Overnight
Magneto was not always Xavier's ally. Though the two were friends, they did not share the same ideals, and for good reason. While Professor X grew up relatively wealthy and possessed a gift that allowed him to see humanity's fears toward mutants, Magneto was a Holocaust survivor and could only see the absolute worst humanity had to offer, without having the benefit of a gift that would allow him to be sympathetic. Magneto must abide by Krakoa's rules ("Murder no man" among them), but that was not always the case; a telepathic Magneto could eliminate humanity with a single thought.
Magneto has mellowed out somewhat over the years, but his hatred for human systems of government remains (if not for the individual human). The fact that Magneto has always seen his gift as a weapon rather than a way to save others speaks volumes about how his experiences during the Holocaust shaped his worldview. The X-Men are quite fortunate, as Professor X has said, to have a Magneto who can move metal and not one who can control mutants - and humans - with a single thought.
