>It isn't so much as the rest of the world having easy access. It is what the Chinese want the rest of the world to see.
If your prosperity depends on using technocracy to deny 1.3 billion people the ability to communicate and share ideas with your citizens, a few things are true:
1) You have created a digital iron curtain
2) You are doomed because information wants to be free
3) If you succeed the result will be war, the only thing left when communication breaks down
"Information wanting to be free" is a concept less rooted in idealism and more in a cynical view of human nature. Even the most closely guarded secrets eventually leak, and as the utility of knowing the secrets increases, the pressure to leak also does. The physical universe itself appears to favor disclosure and abhor secrecy.
>With modern technology we may be creating systems that end up imprisoning our minds for generations with no escape
That has been the goal of authoritarians for a long time. Orwell's vision of it involved obliterating even the capacity to think or speak about anti-state themes.
2) Why?
I think some people live in movies where the bad guy always loses. Reality doesn't work this way. Bad situations where information is denied from people can last lifetimes.
With modern technology we may be creating systems that end up imprisoning our minds for generations with no escape because you'll be killed the moment your technological monitor realizes you're going to fight back.