The case can be made that the US did not bomb H & N out of any particular sense of additional anger, that they bombed H & N to test two orthogonal designs and that they barely squeezed those tests in ahead of the already scheduled destructtion of H&N following the complete destruction of 72 Japanese cities prior to the H&N bombings.
The other countries that joined the nuclear club all made prominent demonstrations of their ability to build and detonate atomic weapons .. there were > 2,000 detonations following H&N.
Many of those tests, including tests by the British, the French, and the Soviets, killed innocent civilians.
The only demonstrated restraint that I can see was the pivot to full blown MAD strategy .. and that came close to unravelling on multiple occasions.
The Soviet Union - and 8 other countries, to a lesser extent - also poured great resources into their atomic project, and then found the restraint not to use it in anger.