To draw back from the specifics of this war: We must bear in mind that this is what human beings (us) do and have always done. As technology has changed, so we have used it to wage nastier war. Human beings are highly tribal animals and have always maimed, tortured and killed their neighbour.
What has really changed is that, by WW2, photography (still + movie) and sound recording had advanced greatly. As has been stated in this thread, the memory of WW1 was clear in the mind (both my grandfathers were involved, one was at the Battle of Jutland and the other flying SE5a's) and the terrible events of the first ensured better reporting of the second.
Technology, aircraft in particular, enabled a new kind of war and so humans made a new kind of war. Just as they continue to do so today. Lots of 'smart' bombs and missiles kill civilians, by accident or design.