It was specifically about dropping the bombs. I wish I had the book and I could look it up. He said something like 'you had all these lives on the line' and how he respected it was a hard decision to make to drop them.
I have the book here. The only part he talks about the dropping of the bomb itself are these passages (p155-156):
[After the first successful bomb test, all the scientists at Los Alamos were celebrating except one: Bob Wilson.]
> He said, "It's a terrible thing we made."
> I said, "But you started it. You got us into it."
> You see, what happened to me—what happened to the rest of us—is we started for a good reason, then you're working very hard to accomplish something and it's a pleasure, it's excitement. And you stop thinking, you know; you just stop. Bob Wilson was the only one who was thinking about it, at that moment.
> I returned to civilization shortly after that [...] and my first impression was a strange one. [...] I sat in a restaurant in New York, for example, and I looked out at the buildings and I began to think, you know, about how much the radius of the Hiroshima bomb damage was and so forth ... How far from here was 34th Street? ... All those buildings, all smashed—and so on. And I would go along and I would see people building a bridge, or they'd just be making a road, and I though they're crazy, they don't understand, they don't understand. Why are they making new things? It's so useless.
> But, fortunately, it's been useless for almost forty years now, hasn't it? So I've been wrong about it being useless making bridges and I'm glad those other people had the sense to go ahead.
The line "I'm glad those other people had the sense to go ahead" may be the one that seems to praise the decision to drop the bomb. But I think he's referring to the other people who went ahead and made bridges, when all seemed futile to him.
