Note that this level of surveillance is not pervasive throughout the rest of China; this is about a region populated by non-Han Chinese (Uyghurs, a who are Muslim and speak a Turkic language); most han residents are colonists. The Chinese language is the official one but is not spoken at home by most people there. The central government promotes Han migration/colonization of Xinjiang as they do with Tibet.
So I suspect you'd find most Chinese people outside Xinjiang very supportive of this: the government and newspapers describe it as an integral part of China with a terrorist separatist movement no different from, for example, how the government of Spain used to describe ETA, or, without the violence, the Catalonian independence movement).
In addition, every time a western politician claims that "all muslims are evil terrorists" it gets printed in China as support for the narrative that these "security" measures are justified (Uyghur separatists have bombed Beijing and other han cities).
I expect this to be routine in OECD countries within the next 20 years. Hell, I remember dystopian movies always had bizarre, pointless "security" announcements as a way of showing how creepy the future had become and how the future didn't believe in people having time to think...and now that happens in every airport and train station in the world! ===
My second paragraph is simply the situation on the ground. The territory around Xinjiang has been under Chinese control for over 250 years; in the preceding millennia it sometimes has; at other times, as part of various Khanates it's been part of empires that controlled China (just as Tibet has at various times been independent; been under the control of China; and been in control of the emperor of China) So depending on what time point you pick you can justify an argument that Beijing's control of the area is "legitimate" or "illegitimate". I have zero connection to any side (not Chinese, not turkic, not muslim, buddhist, whatever).