The current issue of BBC History Magazine has an interesting article about whether the use of nuclear weapons at Hiroshima and Nagasaki was right or wrong. You get the expected balance, with those saying it was countered by those who say it wasn't.
I say it was. And I'll admit that I say this for an essentially selfish reason. I was born in 1949. The one thing those who say dropping the bombs was wrong always seem to forget is that, if they hadn't been dropped, no more than one or two percent of people born after 1946 would ever have been born. There would be people, obviously, but they would be different people.
We often forget just how random reality actually is. A difference of a single second in when your parents started to have sex, or finished, would have eliminated you and caused someone else to be born instead. Or possibly no one at all. There is only a single moment in all of time when you could have been conceived. The unique person who is you is the result of one particular sperm uniting with one particular egg, and the two of them would never be in the same place at any other time.
Okay, strictly speaking, the egg might be there for a day or two. But that particular sperm would never have been there before, and could never be there again. Even on that day, it was one of somewhere between forty and sixty million racing each other for the privilege of fertilizing that egg.
So here's the thing. If the bombs had not been dropped, based on the plans that were in place at the time, when the invasion of Japan came, my father would have been among the first to hit the beach. Statistically, that also means he would very likely have been one of the first to die. If he had, my mother would have married someone else and I wouldn't exist, nor would either of my siblings. If I didn't exist, my children wouldn't exist. That single death on a Japanese beachhead would have wiped out hundreds of potential future generations.
Now, multiply that by all the others who would have died in the invasion. Casualty estimates went as high as half a million Americans. The Japanese were apparently willing to accept civilian casualties in the millions. So the very act of invading Japan would have effectively wiped out every Japanese who was conceived after the war.
The world, to be sure, doesn't care. If none of the people living today had been born, others would have been. Maybe fewer, maybe more. There's nothing special about any particular person being alive. Conception isn't part of a divine plan, it's just the random junction of two haploid cells starting a pattern of replication molded into its current form by millions of years of evolution. You're not really here because God wanted you to be; you're here because one sperm was a microsecond faster than the one that would have produced someone else.
Because this all depends on timing, right down to the second, or perhaps even to the millisecond, any event that disrupts one event will inevitably cause some other event to occur instead. When it comes to conception there was one chance, and one chance only, for the people who are alive now to have been conceived. A world without nuclear attacks on Japan would have seen different couples making different babies.
So, if you're an historian, and someone asks you if dropping the Hiroshima and Nagasaki bombs was justified, and if you were born after the first few months of 1946, the only answer you can reasonably give is "yes," because it's the only answer that would allow you to exist to be able to say it.