As usual, EH, you bring it down to the nitty gritty. I don't know if I could pull the switch, either, even given a perfect justice system. As it is, though, I don't think anyone should be pulling the switch on anybody else.
The fact that I eat meat, which must be killed, is a separate issue. I can't live without killing something to eat, whether it be animal or vegetable. I don't know, but I might, under the right circumstances, be willing to eat human flesh in order to survive, but that's pointless conjecture. The bottom line is that I know I must kill to survive.
Baruch has reason to wonder why one would not assign the power of execution to government when we assign it to police or military. It's a good question, easily answered. Execution is against the law for police; they may only use deadly force when deadly force is immediately threatened against them or someone else. Similarly, we in liberal democracies enforce strict rules of engagement on our military, all of which preclude execution that hasn't been sanctioned by a duly constituted military tribunal.
In other words, capital punishment (execution by the state) of non-combatant private citizens does and should have a different meaning for us than the meaning of civilian death by police officer or death in war.