Ultimately, they are sufficiently confident in their indoctrination that they are unafraid that exposure to other ideologies will lead to a rejection of their own. Where they are not confident, they do limit travel. See their cancellation of passports for Hong Kongers.
I will not respond to your whataboutism argument as it is beside my point.
The govt is confident that most citizens will see the downsides of democracy and how it leads to much social divisiveness and govt dysfunction as evidenced by the US.
HKrs fomenting riots/violence and breaking the law have rightfully had their passports confiscated to face consequences of their actions.
I will not respond to your whataboutism argument as it is beside my point.