TheMagneto, who thought humans needed to be ruled by mutants. However, he never thought that humans and mutants could live peacefully together.
Xavier met Moira MacTaggert years before he created the X-Men. In House of X, Moira is revealed to be a mutant with the power to be reincarnated and retain her memories of her past lives. In each of these previous lives, Moira has tried every different way she can think of to create Xavier's dream of mutants and humans living peacefully together. Instead, she has found that everything she tries leads to the mutants' extermination. Now in her tenth life, Moira decides to show Xavier the truth of his dream before he even creates the X-Men. Xavier reads Moira's mind and sees how all of her choices to save the mutants lead to their destruction. He now believes that the only way to keep the mutants safe is to keep them separate and not have them live together with humans. Even though he says that his dream is still to have mutants and humans live together in peace, he no longer believes that.
Looking back on the history of the X-Men, Xavier's lie about peaceful coexistence is apparent. He has the X-Men live separated from humans in his mansion. His explanation of this is so that they can learn to use their powers. If he did believe in coexistence with humans, he would have his students attending school regularly with humans. Or conversely, he would have other humans living at his mansion. He kept their identity hidden for years because, as he claimed, the humans would hate and fear them if they knew who they really were. If they had integrated more fully, humans might have learned that they were people just like them underneath their powers.
Xavier would have also had to keep this lie a secret from Magneto. They clashed and fought each other many times because of the supposed differences in their beliefs about coexistence. Magneto appeared to feel that mutants should rule over humans from the beginning of the X-Men's formation. All the times that the X-Men were fighting Magneto or the Brotherhood of Evil Mutants, Xavier would have been risking his students' lives for a lie.
Now that the mutants have formed the mutant nation of Krakoa, all pretense about Xavier's dream has been dropped. He has announced to the world that humans and mutants can not live peacefully together and mutants need to live separately. There are no provisions for any humans that are friends or lovers to them on Krakoa. There have been plenty of human and mutant couples in the past, but this is no longer the case. Under Xavier's guidance in House of X, the mutants are now only about themselves and any glimmer of hope of peaceful coexistence has vanished. House of X shows that Xavier's beautiful dream of the peaceful cohabitation of mutants and humans that the X-Men fought so hard for was nothing more than a lie.
