This article analyses the liberal ethics of non-interference in social choice. It examines a liberal principle that captures non-interfering views of society and is inspired by John Stuart Mill’s conception of liberty. The principle expresses the idea that society should not penalize individuals after changes in their situation that do not affect others. The article highlights an impossibility for liberal approaches: every social decision rule that satisfies unanimity and a general principle of non-interference must be dictatorial. This raises some important issues for liberal approaches in social choice and political philosophy.