China investing into US companies is completely separate from the IP issue. For all intents and purposes, once you've bought a company, you've bought its IP.
Buying a company is about the most legal way I can think of, for acquiring IP.
Again - how does allowing foreign ownership of companies in your country harm your country? You mention IP - but it's not your country's IP - it's a particular company's IP. If its owners want to sell it, why does it matter if they sell it to an American, or a Chinese investor?
