You're not totally wrong, but we are not and have never been exempt from war crimes. In fact, I don't know any country half so honest about acknowledging them. This thread is tacit evidence.
I'll be more sanguine about your position (after all, it is our own system which exposed, documented, and is punishing already) when other outfits, like the Serbians still in power, Kim Jong Il, Saddam, the Janjawit, Hamas, ETA, Indonesian army, are hauled over the coals as you seem to think we should be.
Have a great weekend