Maybe he should take it up with Almighty God:
And surely I will require the life of any man or beast by whose hand your lifeblood is shed. I will demand an accounting from anyone who takes the life of his fellow man: Whoever sheds the blood of man, by man his blood will be shed; for in His own image God has made mankind. (Genesis 9:5,6)
Is this one of those doctrines that Catholics are not allowed to dissent against, or are they allowed to believe different?