You have got a fair point about the over population and other problems tourists may suffer if they visit China in large enough numbers. Also, I don't know whether you are aware of it or not. but there seems to be some health concerns with Chinese street food, about the way they recycle the oil and things similar to that.
You can search "gutter oil" on the internet if you feel like.
Perhaps instead Chine people would prefer Japan, Taiwan or Vietnam?
It would be refreshing to see some World Cup in an oriental setting this decade.
It will be wrong to use one-off incidents to tarnish the entire country. I have seen the video of "gutter oil scandal", but I don't know how authentic it is. Anyway, China is a huge country with a population of 1.4 billion, and isolated incidents can't be used to generalize the nation. Personally I would love to see FIFA world cup being hosted by China. If Japan and South Korea can host the tournament, then why not China? And I don't think that tourists will face any issues related to food, as a lot of US-based fast-food outlets are available at every nook and corner of China.
China is a totalitarian dump, and food has nothing to do with it. Read, for example, the monstrous story about Peng Shuai - this tennis player (moreover, world-famous) simply disappeared when she accused an official of sexual violence. Imagine what happens to ordinary people there. I don't think there should be any international competition in shitty countries like China.