The sovereign legal authority of any government derives from its monopoly on violence. If, at the end of the day, men with guns will not come to your home and force your compliance, then the "law" is nothing but paper.

The ICC could never be anything but what it is -- powerless against those with bigger guns. This is the fundamental nature of law and power. Barring the subjugation of all states to a supranational sovereign capable of universal enforcement, there is, ultimately, no such thing as international law.