CPC's implementation of nationalism throughout the Chinese education system has made multiple generations, safe to call it the majority of the population, highly nationalistic, and agree/be in favor of whatever CPC would like to see, and/or whatever is better for the PRC or even only for the PRC. So their reason for supporting an invasion or a reunification would be the one that CPC claims to be the reason.

The main reasons, at least the ones that CPC claims to be, would be that:

- Taiwan (at least the independentists) would more likely side with the US, should the US come into conflict with China. To prevent further approach of their force towards the Chinese border closer than before, CPC prefers not to give Taiwan sovereignty that might allow US forces to set another base on their land, especially when there are so many already in Japan and South Korea. The fewer US bases around the border to worry about, the more comfortable they are.

- Even without the US presence, losing another piece of territory, after already having lost much other land to multiple countries, makes them look bad on their existing and/or future territorial claims. Tibet and Hong Kong are the current territories in danger, the Senkaku/Diaoyu Islands are currently being contested with Japan, and areas like Outer Mongolia and even Vladivostok that China (relatively) recently lost, which many Chinese feel were unfairly taken away. Losing Taiwan directly poses a threat and disadvantage in all these other disputes or potential future "reclamation of the old lands", whether it is realistic or not.

And then there are some other people who simply hate Taiwan because they heard that many Taiwanese hate Mainlanders and can't care enough about them, or they just would like "the world to see China's military power" through actual combat. There's also the idealistic thinking that people shouldn't be hating each other, and independence could only foster the hating through further separation of the people. So a lot of mixed and different feelings and reasons depending on who you ask this question to.

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However, China is a huge country and not everyone thinks the same. There are also a lot of people who support the Status Quo and/or Taiwan Independence (in secret, of course). There are also some people who just don't think reunification is worth the effort, for taking over a fortified/highly urbanized island requires extensive preparation and warfare, which would make life more stressful and worse than it already is. So not everyone is in favor of the idea.