The Nuking of Japan

[Anomalocaris]

There certainly can be group responsibility, particularly if one takes a consequentialist view.

The military exploit the efficacy of group responsibility all the time during training and in establishing Esprit de corps.

Quite, but how would you deal with it justly?

Blame the Japs, or blame the Yanks and Limes?

Blame is a tool, not an end.

Forget about "justly" as some sort of principle. Think of it as an regrettable foible or eccentricity that may be necessary to humor at times, and can be safely ignore at other times. Keep eyes on the ball of acheiving the least bad overall consequence.