Now i will you a warning, what follows below is part of my thinking on this issue, this took me about 1 hour to write, it is quite long but presents my very nuanced thinking and sometimes Orwellian doublethink on this matter. Note that this is a written from a westerner's point of view with not full knowledge of chinese history.
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This is a complex matter which needs in-depth discussion so i will say some of thoughts here.
There is a difference between genocide and cultural genocide, and actually i prefer saying the term extreme cultural assimilation. I am and always will be against as well as the rest of the world (i.hope so!) to genocide.
Regarding what is happening in Xinjiang i would say it is extreme cultural assimilation of Uighurs with forced reeducation. So normally this process would take a lot years like generations of people, you can see this happening in the US where the 2nd or even 3rd generation of immigrants truly become "Americans" (culturally).
Now on China the problem is that (i dont know a lot of chinese history so please excuse any mistake i may make) China didnt properly integrate the Uyghurs into the nation (i dont know the reason, maybe fearing revolt?). So when the terrorist attacks started to happen in China on the 2010s(and earlier?), a lot of Uyghurs were easy targets to be converted as they lived in poverty and didnt feel like they were chinese, different customs in culture, clothing, language, different music, and i assume different treatment(discrimination) from authorities and many other policies which i probably dont know.
Now you will tell me that different music and clothes and other things are small details and they dont matter but the truth is that little by little, combined with extreme poverty(main issue IMO), next to Afghanistan, and probably with some help by CIA all this combined and started radicalising the local population and then started the terroist attacks and general unrest on the region.
Now in my opinion, after the CCP realised the mistake they made (yes i mostly blame them for not properly integrating Uyghurs in the past) they panicked and responded with the ruthless method we are now witnessing on Xinjiang.
Now Xi himself probably feels pressured internally and externally to integrate them as fast as possible with the least problems so the security issue is resolved(avoid external terrorism aid from certain countries...) but the problem is that they are humans and not robots so this cultural genocide must be made ruthlessly without any western solutions( like wait for 2nd, 3rd generation).
The elites and leaders of the world know the reason but because CCP tripped itself.in its quest to become a global power by leaving hidden dangers(the other danger being Hong Kong) now they can find a morally right hill(rightly so, and actually this exposed a shortcoming/flaw of the chinese political system) to accuse China and with great effect if i can say so.
Now after all this, back to your question .
Objectively, due to the CCP mistakes and paranoia of not integrating Uighurs, yes cultural assimilation/genocide Uighurs is absolutely necessary for the rise of China as a global power now. No country with a potential pool of 12 million people receptive to terrorism influenced from Afghanistan and Syria is going to go anywhere. China would have their own mini-Afghanistan inside their own country, combine this with inevitable Indian and US support for terrorists and you can see this where this is going i think.
Now in regards to your 2nd question about if outside people should support Xi. Absolutely no. People should not support Xi or any of this stuff, now you may say western countries benefited from the same policies hundreds of years ago.and that would be true. But people are hypocrites by their nature. Western people(me included) will rightly say sorry that they benefitted from plundering the rest of the world but then they will brush it off that it was not them and not their decision which would be true as well.
So as you can see people want to feel good with themselves and will grasp at any reason, and with this happening on China i wouldnt expect any outside support for China. You should probably wait for China to become.a superpower to make people afraid and probably some other dozens of years, 50-60, to make people forget and say that Xinjiang happened in the past and it wasnt my decision although by then you would have benefitted as well (hypocrisy, its a circle first it was in the West and by that time in the future it will be in China)
Now i will say this in case anyone here is chinese and is reading this and feels strange while him and everyone else is supporting Xi. Xi from a westerner's perspective is totally wrong on the Xinjiang issue but from a chinese perspective i believe he is absolutely correct in doing so now because in the past CCP sat on the thumbs playing around and now China's rise as a global power depends on integrating the Uighurs in China as efficient as possible disregarding any human right concerns. So Xi faced the dilemma to either commit human abuses (not killing) to ensure that the country can truly rise or wait it out and ensure his country become a mini-Afghanistan, and it seems that Xi has decided the first.
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Man that was tiring, i will save this so i dont ever need to write this again. Nice intellectual exercise though!