Every country has laws about who can get passports. In countries without proper rule of law this is often arbitrary. Does that mean all those countries have made emigration illegal?

If the law also says you can't leave without passports, like Chinese law, then yes, obviously.

> If the law also says you can't leave without passports, like Chinese law,

Other countries don't let you in without a passport. Even in the absence of a Chinese law, an airline would deny you boarding if you didn't have a passport.