Call of Duty was the first franchise that came to mind for me as well. I think it was Modern Warfare II which had a mission where you walk through a mall and shoot as many innocent civilians as possible. While I do think that could potentially be a line crossed, the developers do offers players the option to skip the mission due to its controversial nature. A great idea on their part, of course, to judge them as you will. I played the mission because I assumed it added important things to the campaign story, but I felt sick doing it.