Indeed, Sassoon didn't return to the war and only escaped a court-martial as a result of his being declared unfit for service and treated for shell-shock.
Transcript follows. Image courtesy of Wikimedia.
Lt. Siegfried Sassoon.
3rd Batt: Royal Welsh Fusiliers.
I am making this statement as an act of wilful defiance of military authority because I believe that the war is being deliberately prolonged by those who have the power to end it. I am a soldier, convinced that I am acting on behalf of soldiers. I believe that the war upon which I entered as a war of defence and liberation has now become a war of agression and conquest. I believe that the purposes for which I and my fellow soldiers entered upon this war should have been so clearly stated as to have made it impossible to change them and that had this been done the objects which actuated us would now be attainable by negotiation.
I have seen and endured the sufferings of the troops and I can no longer be a party to prolonging these sufferings for ends which I believe to be evil and unjust. I am not protesting against the conduct of the war, but against the political errors and insincerities for which the fighting men are being sacrificed.
On behalf of those who are suffering now, I make this protest against the deception which is being practised upon them; also I believe it may help to destroy the callous complacency with which the majority of those at home regard the continuance of agonies which they do not share and which they have not enough imagination to realise.