I don't get why that's a great argument rather than a silly word game. It's legal for the State to do plenty of stuff that it's not legal for private citizens to do.
This is at best an argument against having poorly-thought-out laws like "Anyone who intentionally kills another loses his head", not one against the death penalty in general.
This is at best an argument against having poorly-thought-out laws like "Anyone who intentionally kills another loses his head", not one against the death penalty in general.