Fight Fire with Fire

Have you ever heard someone say that you should "fight fire with fire"? This strikes me as a bit strange. How does it makes sense to fight a force of destruction with that very same force of destruction? For example, let's say an emergency room doctor is trying to save the life of a man who has been shot several times. If you take the "fight fire with fire" logic then the medical strategy that the doctor should employ would to "fight bullets with bullets".

I just have a hard time imagining that scenario.

Nurse: He's flat lining! Doctor, what should we do?
Doctor: I'm not losing this one! We've got to fight bullets with bullets. Nurse, get me 50 CC's of hyperdoxatrin and a Glock stat.
Nurse: Here you go Doctor.
Doctor: Thank you nurse. BLAM! BLAM! BLAM!

Call me crazy, but I think the phrase should be "fight fire with WATER".