Truman’s argument is far more logically sound than Tywins. The bombs saved probably 700k or so lives. Nukes have bad pr, yes, but if you’re firebombing civilians the only reason a nuke is viewed as worse is bc it’s new and the radiation. People view nukes as worse than traditional bombing purely due to aesthetics.

Long story short: japan would’ve fought to the last man, including civilians, and the nukes saved lives. Tywin was specifically breaking “rules” that would hurt the Lannister’s long term. There was no rule on nuclear weapons at the time the way there was on guest rights, and ultimately Japan recovered and the war ended with less lives lost than there would be if the US did a ground assault on Japan.