Minor spoilers in the question - you might want to skip this if you haven't seen the movie.
In the climax of X-Man: Apocalypse, Magneto is wreaking havoc (pun intended) on the Earth. Magneto is causing magnetic destruction around the Earth, destroying bridges, sending cars flying, boats capsizing, etc, etc. These actions must have caused the death of thousands, if not tens of thousands of lives, or even more.
In X-Men: Days of Future past, he hated Eric for (supposedly) killing one man, President Kennedy. While I can understand Charles might forgive the murders of the men who were present at his wife and daughter's death and at the factory (although Eric didn't kill the men, even though he intended to), why is Charles so accepting of Eric's genocide at the end of Apocalypse?