The beauty of staging a grand entrance would be that the X-Men's opinions and/or knowledge of his allegiances wouldn't mean squat. Let's say the dude *thinks* of Slaying the Light and Ushering a Dark Age of Eternal Terror and Suffering™ 24/7, but he's always saving kittens, making cutesy speeches and taking silly photos with the folks visiting the Treehouse. What on Earth could the X-Men do about it?
Alas, we'll probably just get matching outfits.