The US constitution frequently prevents the US government (and US State governments) from enacting laws or enforcing previously enacted laws. This can be good or bad depending on your point of view, but it's a simple fact that in the US we have constitutional rights that are actually pretty potent. Do the police in China have to read people their rights? Guantanomo is a travesty, but it's a travesty precisely because the US Constitution is difficult for the government to ignore.
A more interesting example is many former British colonies, such as Australia, and Britain itself manage to have quite free societies despite having almost no constitutional protections. In China I'd say you don't even seem to have the basic rights people in the English system and its descendants enjoy thanks to the Magna Carta (Habeas Corpus, for example, or the right to a fair trial. Wasn't there just a very high profile case in China where the accused was very vocal one day and then suddenly had nothing to say the next?)