A major item is the prevention of the proliferation of nukes.
The U.S. has security agreements (or assumptions) with allies. If the U.S. appears weak, then allies freak out and nuke up. China and Taiwan are nearly at war. If the U.S. doesn't come through for Taiwan, then everyone gets nervous. Japan and S. Korea likely get nukes the fastest, since they are tech powerhouses. Then European countries may follow suit. Then, each enemy of every new entry to the nuke club also feels pressure to get nukes. Next, everyone gets in a race to build more nukes.
Additionally, you get the same issue as with Russia. If a big power takes a smaller power, then where do they stop? What is to stop them from taking everything. And this is already happening. China has been in low level clashes with the Philippines to take forcefully reshape borders. If they do this to Taiwan and the Philippines, then they likely will do this to every country in a border dispute with China. And Taiwan is strategically important. Japan faces a greater threat from a China controlled Taiwan. That's why China wants Taiwan. The island is important to China's national security.
In this world, you have a nightmare situation of more fingers on more triggers. More MAD targets for everyone. A greater possibility that someone actually pulls a trigger. And the thing is, China doesn't care about this. If every country on the planet being nuked up was the price to pay for domination, then so be it.
You don't need a citation. You can see from their actions. And China isn't going to come out and say this anyway. But the leaders of the country know what the results would be, and still they continue with an aggressive posture vs Taiwan and the U.S.
The U.S. has security agreements (or assumptions) with allies. If the U.S. appears weak, then allies freak out and nuke up. China and Taiwan are nearly at war. If the U.S. doesn't come through for Taiwan, then everyone gets nervous. Japan and S. Korea likely get nukes the fastest, since they are tech powerhouses. Then European countries may follow suit. Then, each enemy of every new entry to the nuke club also feels pressure to get nukes. Next, everyone gets in a race to build more nukes.
Additionally, you get the same issue as with Russia. If a big power takes a smaller power, then where do they stop? What is to stop them from taking everything. And this is already happening. China has been in low level clashes with the Philippines to take forcefully reshape borders. If they do this to Taiwan and the Philippines, then they likely will do this to every country in a border dispute with China. And Taiwan is strategically important. Japan faces a greater threat from a China controlled Taiwan. That's why China wants Taiwan. The island is important to China's national security.
In this world, you have a nightmare situation of more fingers on more triggers. More MAD targets for everyone. A greater possibility that someone actually pulls a trigger. And the thing is, China doesn't care about this. If every country on the planet being nuked up was the price to pay for domination, then so be it.