This is one thing I disagree with many liberals on, as I think that in a historical retrospective view, the invention of nuclear weapons, ironically, ended up saving more lives than they took. I know this stance makes me an outlier, but there are reasons for it.
First, there are the bombings of Hiroshima and Nagasaki, the first and only times nuclear weapons were ever used in war. I'm aware of the reasons why people have condemned these bombings, as nearly everyone does whenever a discussion of WWII comes up. However, I later realized it's a lot more complicated than the black and white conception most have. The Japanese front of the war had become increasingly bloody, and Hideki Tojo was more than willing to continue his campaign, as well as the horrific atrocities conducted against Chinese civilians. When the United States deployed nuclear weapons, it brought a quick end to the war, and likely ended up saving lives on both sides. Yes, Hiroshima and Nagasaki contained civilian populations, and it's never ethical to intentionally target civilians, but the cities were not arbitrarily chosen. They were primarily military targets, integral to Japanese industry, and were slated for conventional bombings had nuclear weapons not been used. Often in war, nations are forced to choose between the less horrible of two horrible options. The firebombing of Tokyo killed more people than the nuclear bombs did.
A lesser known fact about the war is that Tojo actually murdered more people than the Third Reich. Everything that happened in German concentration camps happened in Japanese camps that were used for the same exact purpose, and the Rape of Nanking was just a fraction of the democide carried out against the Chinese. As a reminder, on the German front, the US was in a race with the Nazis to split the atom first, and there are very few people I know who would have objected to dropping an atomic bomb on Hitler and his legions of Nazis during one of their public rallies.
The second major historical event involving nuclear weapons, specifically their proliferation, was the Cold War. Perspectives differ on whether it was a war of ideas, or a war of nuclear brinkmanship, but now that there's been some historical distance from the end of the Cold War, it's become easier to see how it could have been much worse. The USA and USSR were never involved in a direct war with each other, because both possessed nuclear weapons and knew what would happen if they launched an invasion on the other's shores. Instead, the Cold War consisted of a series of smaller skirmishes within nations and territories controlled by either side. The Cold War lasted from the end of WWII, when both nations had arisen as the world's new superpowers, to the fall of the Soviet Union. That's a rather long time span, and historians are now realizing that without nuclear deterrence, there would have been nothing discouraging the two nations from firing conventional weapons at each other and killing millions of people. It's likely that the damage to both would have been catastrophic, the world today would be a much less stable place, and the war would still be ongoing as we speak. We have enough conventional bombs to destroy the world once over, and ironically, the reason this hasn't happened is thanks to the most destructive weapons ever invented.
Nuclear weapons today remain a contentious issue, and for good reason. It's almost unthinkable that humankind has invented, stockpiled, and at one time used doomsday weapons capable of wiping millions of people from existence in the blink of an eye. There is the threat of rogue nations or terrorist organizations not tied directly to a single nation gaining possession of nuclear weapons or their components; if they believe they have nothing to lose and aren't afraid to die, then mutually assured destruction isn't going to work on them. That said though, there's a reason why this hasn't happened and likely will not happen. Every terrorist still has a homeland that they care about and loved ones they believe they're protecting. Every dictator, no matter how insane or unpredictable they may seem, still cares about their people and their nation. We thought Saddam Hussein was unhinged and chaotic, since he used chemical weapons on his own people and threatened to do so against US troops, however when we threatened him with our own weapons of mass destruction, he decided he'd rather keep his ass intact and got sane real fast.
The fact that no nation is truly safe from a nuclear strike, and that human beings are frail and vulnerable, is scary. Yet this is precisely the fact that even the worst dictators on Earth are keenly aware of. They may pretend they're invulnerable and all powerful, but a nuclear weapon will do the same thing to them as to one of the commoners they oppress. They are not gods, they are mortal, and there are things they care about and fear just like everyone else. This is why dictators boast and show off their military, why they build grand monuments to overcompensate, and why they try to create the illusion of strength through force. They are cowards, and have the most to lose.
Again, I know very few people will agree with me, but one thing in particular changed my mind on this issue. In Japan, since the end of WWII, there has been a historical revisionist movement going on that insists Japan was the innocent victim; it got attacked with doomsday weapons and had done nothing wrong. It's very similar to Holocaust denial, except it's more widespread, with some scholars trying to get all references to Japanese atrocities stricken from history textbooks. The reason this has happened is likely that the Japanese war criminals were never punished after the war, unlike the Nazi war criminals at Nuremberg. There are some Japanese scholars who are pushing back against the deniers, but the cultural attitude is very deeply rooted. There are myriad stories (anime, manga, video games) with a post-apocalyptic theme based on this idea that Japan was the victim, where the horrors of nuclear weapons are hammered home, yet there's absolutely no mention of the things Japan itself did to other nations. Whether intentional or not, I can't help but see shades of the historical revisionism in this cultural attitude. My own family is of Chinese ancestry, so there's a personal reason why I get offended by this, even though by and large I'm actually a huge fan of Japanese culture. I support the scholars and historians brave enough to fight for the truth, and my favorite stories are the ones that have an anti-war theme in general.
War itself is the problem, not the weapons used to fight it. If humanity fought fewer wars, then the weapons and technology of the time would be a moot point. Fortunately, this seems to be the trend.