Homo Homini Lupus
"Man is a wolf to man."

popular Roman proverb by Plautus (dead 184 B. C.), in his Asinaria.
Thomas Hobbes later used it in his "De cive, Epistola dedicatoria"

"Only part of us is sane: only part of us loves pleasure and the longer day of happiness, wants to live to our nineties and die in peace, in a house that we built, that shall shelter those who come after us. The other half of us in nearly mad. It prefers the disagreeable to the agreeable, loves pain and its darker night despair, and wants to die in a catastrophe that will set back life to its beginnings and leave nothing of our house save its blackened foundations."

Rebecca West
Black Lamb and Grey Falcon

"Man's destructive hand spares nothing that lives; he kills to feed himself, he kills to clothe himself, he kills to adorn himself, he kills to attack, he kills to defend himself, he kills to instruct himself, he kills to amuse himself, he kills for the sake of killing. Proud and terrible king, he wants everything and nothing resists him... from the lamb he tears its guts and makes his harp resound... from the wolf his most deadly tooth to polish his pretty works of art; from the elephant his tusks to make a toy for his child - his table is covered with corpses... And who [in this general carnage] will exterminate him who exterminates all others? Himself. It is man who is charged with the slaughter of man... So it is accomplished... the great law of the violent destruction of living creatures. The whole earth, perpetually steeped in blood, is nothing but a vast altar upon which all that is living must be sacrificed without end, without measure, without pause, until the consummation of things, until evil is extinct, until the death of death."

Josef de Maistre