Conduct a long string of practice murders, and then wrap it up by killing the main boss/father/authority figure. Is that the actions of a hero? Since no one can think of any other plot for a video game, good guys do it too and simply claim 'those guys' are barbarian-mutant-zombie-robot-aliens. Yep, clearly heroic and good by comparison.
Bioshock:Infinite and The Last of Us both dispense with the sordid amount of distasteful fakery necessary to claim that such actions are heroic, and just cast the player as a villain.