Why a cautionary tale? The manhattan project was a succees. Does anyone doubt that if a similar war broke out nukes won't be used?
Just look at the number of civilians the japanese killed (nanjing massacare is arguably worse than the holocaust) and they would have kept doing that. Assuming all lives are equal, nukes saved a crapton of lives.
I think it is hypocritical to say cluster and fire bombs that have high rates od civilian casualty and even chemical weapons were ok but nukes somehow are not.
Moreover, can you imagine the world we would live in without nukes? A whole lot of countries would be fighting a whole lot of wars were it not for the fear of starting a nuclear war. Even now, without nukes, do you think there is a chance the US would be attacking Russia over Ukraine? Or if there is a war with China, do you think there would be more or less casualities if there was no nukes? Short of multipe nukes hitting multiple cities on both sides continually, a drawn out conventional war would kill more people, especially with other WMDs still in play. Cholrine gas was used on civilians as early as WW1.
You gotta understand, in a major war like WW2 where losing means nazis and imperial japanese invade the US homeland, most people have no problem nuking their cities (self included). Youe choice is between your children and family or theirs. This isn't like vietnam/iraq/afghanistan which are wars of ideology and interference not wars of self defense. Also keep in mind that most japanese would have fought tooth and nail (civilians included) against an american invasion. Many killed themselves and their own families simply because their land was invaded and they felt dishonored.