It's funny how many people speak of "murder" when they don't even know what that word means. There has to be an intention to kill a person. Xavier invaded Utopia with an army of Avengers and X-Men, then he tried to shut down the mind of the Phoenix host. Cyclops was attacked and he lashed out. No court on earth would count that as murder. And what he did as Dark Phoenix doesn't count either because he was possessed and driven insane and therefore it wasn't his responsibility. After everything the X-Men knew about the Phoenix, Professor Xavier should have known better than trying to shut down the mind of the Phoenix host anyways.
Cyclops was right, that the Phoenix would somehow reignite the mutant race.