He seems to have suffered the same 'I'll abandon my past beliefs to give Krakoa a chance' plot-required-personality-transplant as all of the good-guy mutants who are equally accepting of him, Selene, Sinister, Shadow King, Emplate, etc. creeping around the island.
A select few seem to have made their saving throw. The Morlocks, a large chunk of whom refused to settle on the island and living in a gated community in Arizona for one (and some Morlocks *on* the island attacked Greycrow in retaliation for the Morlock Massacre!). Sway and Petra, wanting nothing to do with the island *that ate them* and spending their new lives drunk and passed out in Vulcan's room on the moon.
But others? Monet seems just peachy with Marius hanging around. Rachel and Magma, among others, rub shoulders with Selene. Karma, until recently, seemed to have no qualms about Shadow King grooming with young mutants nominally placed under the New Mutants supervision, despite some personal history with the dude. Apocalypse and Cyclops have hung out and had drinks together at the bar, despite a fraught history of one possessing the other and turning him into a Horseman of Death and making him attack his friends.
It's easy to speculate that Charles might have given everyone a dose of mellow with a subliminal psychic broadcast of 'give peace a chance.' Or Krakoa, who is explicitly psychically feeding on all of them, might be blunting the sharp edges and helping keep the peace, as the ultimate predator doesn't want his kibble to go fighting each other and killing each other.
Ultimately, it seems like this blithe acceptance of various genocidal nutjobs and personal nemeses and immortal predators and serial abusers is seen necessary for the plot to continue, whether or not it's got an in-story explanation or not.