Honestly, I don't think it is a bad thing if it is done properly. It can be used to deal with the aging population and some PR points. Given, China's massive population, they will be sinicized in a few generations.
Sinicization isnt that simple. The assumption that sinicization is manageable is as (no offense) dumb as Americans thinking that everyone will abandon their connections to their ethnic homeland and pledge allegiance to America only. Spoiler alert: they don't. The Irish, pre WW1 Germans (during ww1, they changed their names and cultural practices to avoid getting beaten, killed or arrested, so technically cultural genocide happened to them), Chinese, Mexicans, Indians, and basically every immigrant group here in the US support policies that would benefit their own ethnic homeland. As of now, most of these groups' ethnic homelands are on the US's side, so from the surface they are Americanized. But later on, when those homelands start to side with China and the US tries to cripple them, those lines will become cracks and eventually gaps.
Throughout Chinese history, external ethnic groups start to get sinicized when their elites accepted Chinese culture and philosophy and/or basically have their homelands (unless they were nomadic) integrated into China. Even then, they arent fully sinicized (ex: Xinjiang unrests). For Tibetans, they are less sinicized than even Uyghurs since they were conquered. Yes, the US played a huge role in instigating those unrests, but a fire cannot start without a source. It cost China a lot of resources, blood, and time to stabilize those regions. Immigrants and refugees are basically impossible to sinicize thanks to, ironically, modern transportation and communication and purpose. People immigrate or run to other countries mostly for survival, not because they worship you. For example, those Western expats ran to China because they have no economic opportunities in their home countries. Thats why when the Europeans tried to do their Westernization process upon refugees, they mostly failed. In short, I sympathize those refugees, but I would not accept and try to sinicize them. Instead, helping their countries build up their homeland's infrastructure, economy, and security is the best way to go. That not only gives you PR points, but also a future ally and trading partner in the future.