I completely agree...but isn't this what you are also doing too?
I don't think there's a need to feel remorse for ridding society of someone about whom otherwise never give another thought, but who comes to our attention for being a satisfied murderer of innocent people. Supporting the removal of that person from existence isn't the same as wanting to kill anyone.
Similar arguments have been used throughout history. Examples include the early years of the USSR, Andrew Jackson's reign of the US, and Hitler's reign of Germany. Sadly, history has a tendency to repeat itself.