There are many factors that have bearing on the operative word, "indiscriminate".
A very informative article was cited in a recent FR thread entitled, Why Truman dropped the Bomb (Long but a very interesting read).
What ever side you come down on, it is clear that the decision to drop the A-bombs was not taken lightly.
Even with the benefit afforded to retrospective analysis, I'm not sure the decision was altogether wrong.
I'll print it up on my slow, Iron Age printer and read it carefully when I come back from shopping.
Meanwhile, as I understand it, civilian deaths are not collateral if (1) these deaths formed part of your intention, whether as a means or as an end; or (2)the weapon itself was (objectively) indiscriminate, in that its target is everything and everyone within a wide diameter of destruction.
The "reactionary" Alfredo Cardinal Ottaviani and conservative Catholic historian Warren Carroll saw it this way; and they are strictly objective and traditionalist in the way they evaluate moral acts.
I'll try to catch you again after shopping, cooking, and supper!