As for Nuclear weapons. I wish we could get rid of them.
Should any nation have them? no Clearly the world is better off if no one has the power to destroy the planet.
Are there some nations better fit to have them than others? yes despite what you think of the U.S. imagine if Hitler had developed nukes first.
Is it wise to get rid of them while our enemies have them? no because our enemies would take advantage of us weakening ourselves.
As for the U.S. dropping Nuclear bombs on Japan in WWII. This is the reasoning that went into it. From the America's point of view Japan was not going to surender, they were going to fight to the last man and an invasion of Japan mainland would have meant many, many casualties on both sides. The use of the nukes got them to surrender much earlier(I know some say that Japan was ready to surrender but I don't know enough about those rumors/conspiracies to comment). The world in the WWII era were used to death and destuction so I don't think the idea of what these weapons would do had as much of an impact on them as it would on us. I also think people were sick and tired of the war and wanted it over asap, and the nukes did that. I'm not trying to justify it but that is the reasoning.
The ironic thing of about Nuclear Weapons is that by somtimes they prevent wars. Think about it, why is it that the cold war btw the USSR and the USA never became a full blown hot war? Because each side knew that if they went to war it, it would only end it one way by both sides firing their nukes and destroying both nations. There was no way a either side could win a war against the other and to go war with the other was to commit suicide. If the nukes weren't there, each side might have been more temped to go to war because there would have a chance of victory. I am not saying that that justifies the existence of these terrible devices but it is ironic.