Call of Duty: Modern Warfare 2 "No Russian" (2009)
Now this example does not pertain to the whole game. Instead this example is off of a single mission from the solo campaign of the game. In the mission, there is a point where the player must witness his squad open fire on a crowd at a Russian airport as part of a mission where the player's character is aligned with a Russian terrorist group, leaving a trail of bodies littering the terminal while some crawl injured across the terminal. The player never has to fire a single bullet during the act for the mission to progress.
As expected, this is highly controversial because it depicts an act of terrorism, and it has been widely criticized for such content. It is up to the player to decide and be responsible. If they can feel they can handle the content of the mission, they can go on ahead with the mission. Ultimately, the gamer must make the right choice. Take a look at the mission, entitled "No Russian" to see what the fuss is about.