More straight question: why Chinese government should take it a priority to fight the U.S.? Perhaps the people in the U.S. think they are really important and we are here everyday figuring how to fight the U.S. The chief enemy of Chinese government is, frankly, Chinese people. So is the second and third enemy. U.S. lines up the fifth enemy of Chinese government. You are not that important in this decision making.
China blocks western news outlet and facebook; don't have any idea China is doing this to fight U.S., they do it to fight us the people.
That's because westerners (me included) usually struggle and fail to understand China, and usually you fear what you don't understand.
It's quite a widespread sentiment to fear that China wants to conquer the whole world, hence people react to that.
(I'm not saying this makes any sense, mind, I'm just trying to explain why many people think that China thinks we are enemies)