Here, walk with me through an observation. It's generally presumed that people should be left alone, and be free to do what they want, correct? In other words, we presume that anyone farming their fields anywhere in the world would rather be left to themselves than to be told how they're going to live? Okay, which forms of government are the least meddlesome in individuals' lives but still provide for basic security and services, individual freedom (women's rights, religion, etc.) and so on? For the last hundred or so years democracies have had an good track record in that regard, especially in comparison with the Soviet or Communist Chinese systems, (Stalin and Mao didn't help of course). Also theocracies have been shown to be dangerous to human rights, since one belief system is inflicted upon an entire population, many times victimizing women or minorities.
So the idea is this: Western democracy must survive, not because of some idea of 'fairness' or 'rightness', but because once you consider all the competing systems that will otherwise rule the world, it is the least oppressive.
So when someone says they don't want a dictatorship to have nukes, it's perfectly reasonable to say "It's in the best interest of every individual on the planet that western civilization survives, therefore a dangerous dictatorship shouldn't be allowed to have nukes". You're not looking at the fairness between countries, you're considering the welfare of the common individual, anywhere in the world.
Well, it's a good thing that you haven't given those dictators any help staying in power, for example by giving them an obvious external enemy they can blame all their troubles for, not to mention justify tightening their fist, now isn't it?
I'm sure you know dictators have no trouble finding external enemies, no matter the time period or which countries happen to exist at the moment. They don't need anyone's help for that.