Because information -- is a weapon. Mayve the most dangerous weapon in modern world after nuclear. They built Big Chinese Firewall and block sites to protect yours. To protect from lies. Gorbachev in 1985 stopped protecting us, opened iron curtain and let the information to flow free to our hears. It was information attack, real info bombing. As a result, we were fooled by lies and propaganda from our competitors -- USA and Western Europe countries. USSR was ruined and fall into pieces. Do you want your Motherhood -- China to fall into pieces? Your government aims to prevent the same scenario in your country.

In the news in Russia, said that China banned the use Facebook and twitter to protect against terrorist acts and mass protests. In St. Petersburg, some organizations have agreed to twitter and Facebook about the meeting and put up a fight.

Maybe you have to ask your government about it :-). Don’t be sad. It’s seems like democratic values had shown fault all over the world. Our government already have announced that they are creating agency for control internet. The main reason that they sow is a cyber crime, terrorism and a crime connection with ethnic. It's first step.

Maybe you have other version of facebook that your country want you to use and it may expand. cowboy...

Maybe they're afraid of raising a protests and revolution like Egypt and Tunisia , do you ? :)