The author uses the words "theogony," "cosmogony" and "philanthropy" because these are all high-minded topics whose aims in practice are to explain and justify

The author uses the words "theogony," "cosmogony" and "philanthropy" because these are all high-minded topics whose aims in practice are to explain and justify things as they are; Byron is ironically suggesting that morality in this world is confined to academic discourse, without any application in real life, where things remain dog-eat-dog.