I partly agree that a country possessing nuclear weapon can provide deterrence and reduce the risk of being invaded by other countries.
However, things could get much worse if more and more countries started acquiring them. It would create an arms race, and that is certainly not good for world peace. All it takes is one miscalculation or one moment of losing control by a single country. The consequence could drag the whole world into a nuclear war, which could mean the end of the Earth.
Having too many countries possess nuclear weapons would create more risk and harm than benefit for humanity.
That's true, I understand from your angle of reasoning. If too many countries power possess the nuclear weapon, it could likely fall into the hand of a fragile country and one single mistake will cause a lot of disaster. But in the same vein, if it remains in the hand of a few countries, they will continue to intimidate and threaten others.
The best approach could be a powerful check and balance. In order words, instead of thinking about the military and weapons war, countries should start thinking about the economic war which I think China is somehow leading at this time.
But then, be it economical war or military, the less powerful countries will still suffer it. The best thing to do is for countries to improve and strengthen their economy and defence.
Our world has never been truly fair, and it has always been a place where the strong bully the weak. This has been happening for thousands of years, not only between humans but also in nature and between different species. So it's hard to find a solution that can create a fair balance for everyone.
I think instead of countries constantly engaging in an arms race or turning to economic warfare, building a multipolar world could be a better way forward. When power is spread among multiple major power and smaller countries have the freedom to choose sides, it becomes harder for any single country to impose its will on the rest of the world.
That's why I don't expect China to replace the US. Instead, I hope China could help create a multipolar world.