The question contains spoilers, so if you didn't watch the movie, be warned!
During the movie Apocalypse gathers a group of mighty mutants around him. While it seems that some form of mind control might be involved, it does not seem to me that they are forced completely against their will to join him. He gives them greater power and lures them that way. In the end, most of them turn against him. So no strong mind control seems be into place.
Especially the actions of Erik seem to be more out of revenge. He killed a group of (more or less) innocent cops, who accidentally killed his family and he was about to kill his completely innocent co workers out of motives even I could not fully understand. In the finale of the movie he brings great destruction all over the world, presumably killing millions of people (Crushing buildings, bridges, throwing ships through the air and so on). Then because he wants to save Xavier he turns against his new master in the last moment.
After that he does not show any remorse for killing millions of people and is treated by Xavier and the others as a good guy and buddy and allowed to leave as if nothing happens.
Why does nobody make him accountable for the death of millions? Does changing his mind in the last moment and helping to save the world make up for murdering a few millions in the mind of Xavier and the others?
As mentioned, I don't think he does this under mind control completely against his own will (as he was about to kill his co-workser without any influence of apocalypse). And if I lose my famliy and somebody very persuasive seduces me to start mass murdering and change my mind and save the day, I would go to jail I assume and not get away with a "Oops. Sorry. I was not completely myself when I did this."