When you were in China, you were shown only what you were meant to see. There are large portions of China which are unavaliable to tourists.
Nobody forces you to stay with a tour or anything, it's not like North Korea. Of course, if you stick to a guided-tour, you probably won't see too much. If you leave the city, you can find plenty of backpackers.
The friendliness probably has more to do with the culture being more laid-back then political freedom.
Disturbing you have collected 8 upvotes for this utter nonsense. I challenge you to name any area of the country permanently off limits to foreigners. China is hardly perfect but what you insinuate is just BS.
At any other time, though, it should be fine. It's not North Korea.