He is not opposed to the killing he is opposed in doing it on moral grounds. He hates God and anything and everything associated with God, such as morals.
In the New York Time's review of Dawkin's book -- THE GOD DELUSION, they hailed him as :
" a writer who "'understands the issues so clearly that he forces his reader to understand them too."' Recently awarded the distinction of "'public intellectual"' in Britain, Dawkins is Charles Simonyi Professor of the Public Understanding of Science at Oxford University.
I don't know if Dawkins hates morals but he certainly can not logically justify their existence since he denies the concept of free will. How can morals exist in a strictly deterministic system? Answer, they can't and that is a conundrum for the deterministic materialists like Richard Dawkins.