Had MacArthur had his way, Hiroshima would look like a safe haven compared to Pyongyang. He suggested using nukes "tactically" in North Korea to take out strategic infrastructure like bridges and tunnels. But that’s kind of like bringing a cannon to hunt sparrows. This was the US’ most celebrated general at the time on account of his success in the Pacific Theatre during WW2 and enormous success defending South Korea; what he said could really only be overruled by the President, which is ultimately what happened.
The top brass didn’t care about civilian casualties. That much is obvious when they suggest using full-blown nukes just to take out bridges.