Fight Fire with Fire

An expression used meaning "We'll fight the same way they do", usually implying that they are fighting in a dirty or unfair manner.

Fight fire with fire is a technique used in fighting some wild fires. A wide line is intentionally burned in a controlled way, somewhere ahead of a marauding fire and when the fire reaches the line the lack of fuel hopefully stops the wild fire at that line.

"Fight Fire with Fire" is also used as a slogan for prescribed burning even when there is not an immediate threat of a current wild fire. Prescribed burning reduces the highly flammable plant material there by reducing the chance of future wild fires. It can also be used to regenerate forests, grasslands and the wildlife that depend on them.

This expression is oft put to ill use. Many have fought, and decided that because the enemy has done something perfectly barbaric, that they have permission to do it also. In doing so, they forget the principals for which they were fighting, and the battle becomes a simple personal battle between the two sides, purpose be damned. Thus, fighting fire with hypocrisy.