The re-establishment of Chinese sovereignty was a bloody and messy process.
Yes there were huge mistakes during Maos era, just as there have been errors made in many eras of history.
Despite those mistakes and excesses China rebuilt its sovereignty and now is able to deal with the world increasingly on its terms.
Is the USA innocent of how it has historically treated people of colour (ie enslaving them) and still discriminates in many ways and places to this day?
Government is not an easy process, it is messy.
There are internal conflicts and external threats.
If Tibet had not been seized by China then the US would have emplaced nuclear weapons there and China may not have retained its self determination.
Nationhood is a brutal contest for power internally and the ability to project power sufficiently to maintain and grow wealth and prosperity- all nations are confronted by the same essential challenges.