hanged for a sheep (as well) as a lamb, (might) as well be

One might as well commit a great crime as a small one, since the punishment would be the same; also, do not stop at half-measures, but enjoy something to the fullest. This term comes from the times when both sheep and lamb were considered so valuable that the theft of either was punishable by death. “As good be hanged for an old sheep as a young lamb” appeared in both John Ray’s English Proverbs (1678) and James Kelly’s Scottish Proverbs (1721), and has persisted to the present day. See also IN FOR A PENNY, IN FOR A POUND.