I think that's the point. I'm personally not an advocate of this because it seems to be a little too "beat you over the head" with its moral metaphor, but the whole point is that the President should have to personally kill someone to understand the gravity of what they are about to do.
From the perspective of an advocate I'd say: If they can't come to terms with killing one, who are they to execute hundreds of thousands?
From the perspective of an advocate I'd say: If they can't come to terms with killing one, who are they to execute hundreds of thousands?