10 Times Professor X Outsmarted Everyone

After spending years gently taking care of Matthew Malloy - a mutant who was completely unable to control his powers, and thus had to have them suppressed by Xavier's abilities - the leader of the X-Men would be visited by Tempus, who had come back in time to warn him that Malloy would continually lose control of his powers after Xavier died, and would be responsible for killing countless scores of people.

And thus Professor X creates the most beautifully sketchy plan in history, having Tempus take him back to the moment that Matthew's parent met, and then using his own mind-control powers to prevent the two from ever crossing paths - thus stopping Mallow from having ever existed.

It's kind of awful, in the sense that Matthew was a real human who was purposefully murdered by Professor X. While this is true, it's also true that it's a move that basically outsmarts everyone, as it takes out an otherwise invulnerable threat. It also prevents any outrage or backlash from other X-Men by doing so in a way where they literally have no way of knowing, because as far as they're aware, Matthew never existed.