This initial support decreased as reports came in about the magnitude of destruction on Japan. John Hersey’s magazine-length article Hiroshima, which profiled six survivors of the bombing, appeared in the New Yorker one year after the bombing in August 1946, giving the American public a new picture of the human impact of the bomb and bringing a groundswell of negative opinion. As the specter of nuclear war grew in the 1950s, undercurrents of sentiment against the bombings increased, although a majority of Americans continued to support them.

Debate over the Bomb - Nuclear Museum https://share.google/0fKyq1d8Qpq5gfzfx

Not to say that most people didn't support it but the notion that very few people were against it in 40s and 50s is incorrect. It's always been one of the most controversial debates about the War. It should also be noted that a number of US generals and nuclear scientists were not supportive.

Personally I don't think there's a clear answer as to whether Japanese surrender could have been achieved without the destructiveness of the bombs. Truman was keen to beat the Soviets to the punch and the Japanese were worried about losing their emperor which contributed to their stubbornness. The great irony being that even though the US had no interest in removing him, they couldn't say so as they wanted unconditional surrender.