Defend your opponents' rights, or lose your own

An avidity to punish is always dangerous to liberty. It leads men to stretch, to misinterpret, and to misapply even the best of laws. He that would make his own liberty secure must guard even his enemy from oppression; for if he violates this duty he establishes a precedent that will reach to himself.

— Thomas Paine, First Principles of Government (1795)