"The 'Kill Hitler As A Baby' Argument" or "Would You Kill Thousands To End A War?"
 

Truman later said he regretted having ordered the bombs. He didn't know what a nuclear bomb would do, all he had been told was that it was a very powerful weapon that would make the enemy shit their pants with fear. While this story may or may not have been constructed after the fact, it still tells us that using the bomb was wrong, a mistake; just the kind of history we should try to learn from. If we need more than two cities to learn not to nuke people, then we are doomed - literally - and I'd like to think the people with the fingers on the triggers understand that.

Now, if I was in charge of a war, which I hope not to be, I'd try to remember what the more enlightened philosophers said back in the day when most kings went to war if they just thought they could take some land from another king: That the only honorable purpose of war is to destroy your enemy's ability to make war. If you do any less you invite defeat; if you do any more you invite depravity. (Fun exercise: study how this may or may not apply to the Viet Nam war, the six day war, the Gulf war, the Iraq war, the Afghanistan war, the proposed war on Iran, the war on terror, the war on drugs or the war on abortion.)

There are of course innumerable ways to pursue that goal. You could attack your enemy's weaponry, economy, credibility, morale; you could mount a defense that would be impractical for the enemy to attack; you could become the enemy, make friends with them. Killing a bunch of them would be the stupid way, the cheap way, the inhumane way you resort to when you fail to think of anything better. Depending on the circumstances it may be the only responsible way, but that's a pretty silly hypothetical; of course you'd do the responsible thing if it's the only thing you can possibly do that's not irresponsible.

Ever notice how everyone acts responsibly in hypothetical scenarios?

I say hindsight is 20/20. Just because a choice was wrong doesn't mean it was the wrong choice at the time. Maybe there was a better solution, maybe it just would have led to a nightmarish land war, then there are the unknown effects it would have had on the following cold war.

Its easy to look back on something you did and say if you did something else things would have been better, but that doesn't mean you are right. The old time machine monkey's paw trope.

Especially if you consider that a planned invasion of mainland Japan would've resulted in casualty figures into the millions...

I don't know what should, would or could have happened if this or that; I'm saying that no one should want to use nukes again based on how it has worked out historically. Maybe it saved more than it killed lives or maybe not, but the guilt suffered by those responsible and the trauma of its impact on this world - environmentally, sociologically, whatever - speaks a clear message: Anything would be better than doing this again.

RE "Kill Hitler as a baby":

It comes down to you sending into the unprepared past a person with (presumably) advanced technology, or at the very least relevant knowledge of history past that point and the personality capable of murdering a baby in its crib without losing sleep over it.

You know how they say popping a zit only spreads the bacteria out and creates more?

Hey, now.

It didn't kill millions instantaneously. I assume the radiation poisoning would be the only way it got up into the millions.

Given that combined, the nuclear bombing of Hiroshima and Nagasaki didn't even kill between 150,000-250,000 people... and of those figures, only 15% died from radiation sicknesses.

And if we just wanted to kill people, there were other non-nuclear ways to do so, such as firebombing which was far more indiscriminate. And also, the two cities have been rebuilt, and people started living in the destroyed area 4 years after the bombing so the "Surrounding land was made uninhabitable" line is kind of made moot.

While he was probably bummed about the bombing of Japan as well, I know Kurt Vonnegut was always quick to point out that the firebombing of Dresden killed more than that.

Basically war sucks regardless of how you kill the people you're killing. You would be better off not starting a war.

Take the war in Syria, for instance. Honestly I think we are better off not getting involved at this point (the point for intervention would have been when Assad had killed 9000+ civilians, prior to an actual oppositional army being created. because then it would have made more sense as a preventative action), and honestly disarming them of their chemical weapons as opposed to bombing targets is probably a better route, even if it leaves the country mired in civil war. It's already cost 100,000+ lives, I don't think bombing targets at this point is going to reverse the course of that war, probably just exacerbate it.

Additionally, assuming you DO manage to kill Hitler, where do you decide to stop? Why not do the same to Stalin and Chairman Mao and avoid the various tragedies there? Why not off Vo Nguyen Giap and preemptively avert both the Vietnam War and the First Indochina War? Off Andrew Jackson and at least put a stopgap to the Trail of Tears? Off George Washington et al and avert the whole geopolitical morasse that is the modern United States of America? Off the grandparents of that asshole neighbor of yours who blares his stereo at 3 AM and never have a bad night's sleep again?

And even if you don't, how do you ensure others don't as well?