I think they wanted to hear that it’s ok to invade other countries. Despite China being very pragmatic in all matters, China’s view on Taiwan is highly irrational. They want to have it because… well, just because. At the same time they manage to mostly ignore the territories that have been stolen by the Russian Empire. From the practical standpoint they actually have a better chance to regain the Russian territories gradually (through negotiations). I mean, Taiwan can be invaded, but it will be a scorched earth type of invasion making it entirely pointless.
Saying China wants Taiwan “just because” over simplifies the situation.
During the Chinese Communist Revolution the previous government of China retreated to Taiwan. The official name of the Taiwanese government is “Republic of China”, demonstrating that their legitimacy stretches back to this time period.
While Chinese settlers in Taiwan dates back further, China claimed the island in the 17th century. The island was under Japanese rule for about 50 years, before being returned to China in the post WW2 treaties.
The history is deep, and Taiwanese independence is a relatively new thing.
I think it is fair to say conquest of Taiwan has always been an issue of national pride for the PRC. It isn't a national security threat.
It is based on a manifest destiny ideology that the PRC is the only legitimate heir of Chinese culture and history, and sole rightful ruler of all people of Chinese descent.
I would say it’s a potential national security threat. The Taiwanese government does call itself The Republic of China.
From a security standpoint it would be like if a group of US politicians and other elites took over Cuba and called themselves The Republic of The United States. Yeah, an island nation wouldn’t win a fight, but their intentions are in the title.