I don't understand why asking people to eat a well-balanced vegetarian diet is considered drastic, while it is medically conservative to cut people open and put them on cholesterol-lowering drugs for the rest of their lives.
—Dean Ornish, MD
antithesis
A figure of speech in which words and phrases with opposite meanings are balanced against each other. An example of antithesis is "To err is human, to forgive, divine." (Alexander Pope)