Abraham Lincoln on weighing the preponderance between evil and good.

The true rule, in determining to embrace, or reject any thing, is not whether it have any evil in it;but whether it have more of evil, than of good.There are few things wholly evil, or wholly good. Almost every thing,especially of governmental policy, is an inseparable compound of the two; so that our best judgment of the preponderance between them is continually demanded.

Speech in the House of Representatives(20 June 1848)