Apparently getting kicked in the face, getting smacked in the tummy, and breaking their neck are considered the same thing by Ubi.
Just as much as stealthily getting shot in the arm and getting shot in the head.
But at least I want non-lethal option just for fun. Maybe add in a tiny reward for letting them live. And bringing in the cartels/unidad you stowed in your car to a rally point can net you +10 of a supply for each. I mean, why not a little feature like this? When you stowed someone in your car, it is a 'crime' to kill them since they would have been marked as surrendering enemy.
While the original question was prompted by the splinter cell mission, its not just because of said mission. It was a general enquiry. Non lethal options wouldn't take anything away from the game. If anything, it would provide more mission possibilities or role playing options.
In respect to the ui, i grabbed a soldier, it said "knock out", it counted as a kill. If its a kill, it shouldn't be labelled a knock out. Not the end of the world, but a tad misleading is all.