While it was recognized in 1927 that radiation causes genetic damage and increased incidence of other issues later on, there are fairly well regarded arguments that, terrible as it was, the 'shock and awe'-style strike is likely to have resulted in net fewer deaths than a conventional invasion. One response seen often is that the bombs could've been demonstrated on a nearby island, but, like contemporaries of the time, I'm personally of the mind that it wouldn't've been enough to halt hostilities. Conventional bombs wouldn't've been big enough either; the largest non-nuclear bomb used up to that point clocked in at ~6.5 tons; the two nukes weighed in at ~15 and ~20 kilotons (which is nothing compared to current ones-- the Tsar Bomba that Russia tested had a theoretical yield of ~100 megatons).
Still a nasty incident in human history, but it's just one of many in WWII... thankfully still remembered, at least. (731, anybody?)