> but you are precisely reinforcing my point. Because opponents can claim via evidence that the death penalty is effective for this, if you argue on the basis of "facts".

I don't believe I am. The death penalty being effective at reducing a crime isn't itself a sufficient justification of the death penalty.

> Thus, objectivity should not be used as an argument for an ethical and moral human principle. Such principles stand by themselves to maintain the sanctity of the human soul - no justification needed.

We do have objective arguments though; ultimately everything can be quantified by the amount of harm or good it does.