According to a Twitter update from Obsidian regarding its upcoming stealth-em-up RPG, Alpha Protocol, it's possible to complete the game without killing anyone. The tweet failed to elaborate on why someone would choose to play through a spy-action game without killing anyone (but you can bet there's some kinda reward in store for the apprehensive player) and also whether or not it's possible to clear the game without maiming, disfiguring or severely bruising anyone. Frankly, given the nature of the action-spy business, we don't see how that would be possible.
The "no kill" challenge has been posed before, appearing in other stealth titles like Metal Gear Solid and even the straight action-oriented Mirror's Edge. In fact, it would be kinda strange if Alpha Protocol didn't allow players to finish the game without killing -- it's become a requisite for the genre, after all.
Well, however you decide to tackle Alpha Protocol, at least there's some sex in it for you, right?