Its been very useful at doing the same thing the ad hoc international war crimes tribunals that preceded it did but with greater regularity and without as much spinup/winddown costs for each conflict they address.
> The very concept of an International Criminal Court, operating in some idealistic moral space above war and diplomacy,
That's not its concept or where it operates, though.
> If everyone agreed to arbitrate world matters in the ICC, why even have militaries?
I think you’ve confused the ICC with the ICJ or the UN itself. The ICC does not exist to arbitrate disputes between nations in place of settling them by war.
That's… kind of the point? To not have to kill and destroy each other to settle disputes.
Isn't actual law a social contract aswell?
Yet two of the most powerful thugs: Putin and Netanyahu won't go near an ICC signatory state.
Also, if look at the exact plane movements of his visits, they specifically avoid the air space of countries that do take the ICC seriously.
[0] https://en.wikipedia.org/wiki/List_of_international_prime_mi...
[1] https://abcnews.go.com/Politics/netanyahus-jet-largely-avoid...