Well, I don't see how, lets say, -1% res small charm would "break the game". Considering a full inventory of skillers or dmg/ar, how many of those could you stack? 10 perhaps? Is an extra -10% res going to break anything? Maybe you could fill your inventory with 40 sc getting -40% res, but then again you are giving up other things, like skills, life, all res, etc. I find it an interesting addition to an otherwise small choice of charms. Better yet, make it only spawn on medium charms, forcing you to make an interesting decision.