Hinduism...Why did Lord Krishna support unfair means in Mahabharata war?

Lord Krishna was diplomatic.The Kauravas were more powerful than Pandavas.Defeating them was impossible.So Krishna came up with this theory.Arjuna didn't accept the theory initially so Krishna made him understand that the Kauravas were evil souls who were born to raise hell on earth.If they weren't killed they would torture the people.Krishna said that we have to defeat them for peace by using not unfair but diplomatic techniques.