It's a completely fair question to ask what is the Chinese justification.
I found this documentary[1] by CGTN about the recent history of extremism and terrorist attacks in Xinjiang to be useful in outlining some of the context for this.
These terrorist attacks were a real problem and have resulted in the deaths of over 1000 civilians (including Uyghurs). China's argument is basically their re-education "camps" are an attempt to address the underlying causes of this, which is basically economic under-development, lack of education and job opportunities. So China basically identified the people who were involved in these groups and susceptible to radicalisation by them, and set up these schools for them which would teach them skills, including Mandarin, that would help find decent jobs that could provide for them and their families, which eliminates the underlying material basis of the support from some parts of the population that the terrorists may have had.
Having said that, there is still a huge discrepancy in what China says it's doing and what the west claims it's doing. Western sources claim that these are actually "concentration camps" and that there are as many as one or even two million Uyghurs interred there. These allegations are dubious for a number of reasons, but that's a topic for a different post.
Like I said, your question is the right question: what is the Chinese justification for this? And I think it's fair to say their answer is at least plausible on the surface of things and internally consistent. But it leads us to another question: if the claims of western sources of one million plus Uyghurs in "concentration camps" are true, then how does the west explain China's motive for that? China isn't stupid. Why would it put 10% of the population of an entire province in a concentration camp? Are they just that cartoonishly evil? It doesn't really add up to me.
At end of the day repressing restive frontier minority that accounts for less than 1% of population for domestic security (especially terrorism) is the "correct" political decision for CCP. There isn't any feasible calculus for not taming XJ (or Tibet or HK or TW). The real answer is they were left alone for too long due difficult access (whether by geography or politics), granted privileges in hopes they would not stir up trouble. That didn't work, and now wealthier PRC can build high speed rail into their provinces to forcefully integrate. Something every other Chinese province was subject to post 50s. In short, it's simply their turn.
Even the most pessimistic Zenz estimates of XJ internment at 1/12 of population is roughly lifetime incarceration level of US blacks. And the hit job articles on XJ vocational/reeducational "slave" labour programs still have "inmates" paid dramatically better than US prison labour in absolute terms and substantially better in regional terms. Exceeding ~40% of 600M Han Chinese subsisting on informal wage economy. Han Chinese would lose their shit if they find out the amount of subsidies going into XJ securitization and sinicization. If they the the choice between spending trillions to "tame the savage" in XJ versus 12M bullets for an actual genocide, the amount that would pick the latter would be disturbing.
US tried to nation build and spread western values in Afghanistan - PRC is nation building in XJ and spreading PRC values. Just with less bombs and more infrastructure.
Zenz is literally _the_ source of anti-Chinese propaganda. He's the main person behind "Chinese Tribunal", which... well, a private NGO, operating without any legal basis or oversight, calling themselves a "tribunal", think what you will.
I am not saying that it is the case, but let's assume for a moment that China is "re-educating" the Uyghurs to help them "find decent jobs that could provide for them and their families" and so on. Do you think it is acceptable to force someone to undergo "re-education" against their will?
I found this documentary[1] by CGTN about the recent history of extremism and terrorist attacks in Xinjiang to be useful in outlining some of the context for this.
These terrorist attacks were a real problem and have resulted in the deaths of over 1000 civilians (including Uyghurs). China's argument is basically their re-education "camps" are an attempt to address the underlying causes of this, which is basically economic under-development, lack of education and job opportunities. So China basically identified the people who were involved in these groups and susceptible to radicalisation by them, and set up these schools for them which would teach them skills, including Mandarin, that would help find decent jobs that could provide for them and their families, which eliminates the underlying material basis of the support from some parts of the population that the terrorists may have had.
Having said that, there is still a huge discrepancy in what China says it's doing and what the west claims it's doing. Western sources claim that these are actually "concentration camps" and that there are as many as one or even two million Uyghurs interred there. These allegations are dubious for a number of reasons, but that's a topic for a different post.
Like I said, your question is the right question: what is the Chinese justification for this? And I think it's fair to say their answer is at least plausible on the surface of things and internally consistent. But it leads us to another question: if the claims of western sources of one million plus Uyghurs in "concentration camps" are true, then how does the west explain China's motive for that? China isn't stupid. Why would it put 10% of the population of an entire province in a concentration camp? Are they just that cartoonishly evil? It doesn't really add up to me.
[1] https://www.youtube.com/watch?v=pqlzunwilGM