Do you have any more information about Manhattan Project scientists committing suicide? Google doesn't show anything.
Whether Japan had been third world and underdeveloped fifty years earlier has nothing to do with that, at that time, it had invaded country after country and caused huge casualties, starvation, torture and misery. There were many more Japanese who died just as horrible burning deaths in the ongoing saturation bombing by conventional weapons of the country; in fact, it was difficult to find two cities that hadn't been extensively damaged already so the effects of the atomic bombs could be clearly seen.