Lots of action-based games now incorporate some kind of non-lethal option, which is good in theory because it adds a further challenge for players who don't want to go through the game just killing everything in sight, and it gives the option of different endings depending on how much blood was shed - like, for example, Dishonored. It also helps the storyline in avoiding the paradox of a "hero" who goes around killing innocent guards who are just doing their job.
However... a lot of the time, non-lethal options are implemented quite shallowly. In Dishonored and Deus Ex: Human Revolution, the non-lethal attacks are more or less identical to the lethal attacks - firing a tranquilizer dart or knocking someone out from behind is identical to using a silenced gun or knife backstabbing. There's no good reason not to use non-lethal force, and that kind of cheapens the player's decision to play humanely. It doesn't take any extra effort, and so it's not the challenge it should be.
In real life, pepper spray and rubber bullets and such are known as "less-lethal" for a reason - e.g. knockout gas is essentially a nerve agent and can cause serious health problems. Choking someone to make them pass out, shooting a rubber bullet, or using a tazer can all lead to lethal consequences. And no one uses tranquilizer darts in real life because a standard dose will kill smaller people and barely affect larger people.
I've been playing Red Dead Redemption, and there's been several times where I've rode into a gunfight and accidentally shot and killed an innocent person in the chaos. Without an efficient non-lethal option (other than the lasso), it adds a certain gravity to things. In SWAT 4, there are times when you can't rely on less-lethal methods and have to be ready to kill suspects or else risk hostages or your team getting killed. That, to me, seems much more nuanced and realistic than tapping someone on the head and hiding them to wake up with a mild headache.
Should games use more realistic non-lethal options that occasionally result in unintentional deaths? Or is it unfair to players who want a no-kills playthrough?