You are not concerned about North Korean missiles being able to reach the United States with nuclear payloads?
Because influential people in the US want to do business with China. China provides a large pool of cheap labor and low income customers. Many American industries benefit from trading with China. If we closed off Sino-American trade, both countries would suffer.
Well, I think ‘devastate our industries’ is a highly hyperbolic…and untrue to boot. That gets into the whole outsourcing rant though so I’ll let it go at that. The US gets a lot out of trade with China…just as they get a lot out of trade with the US. Currently China gets MORE out of trade with the US, but then we wanted it that way…in fact, we initially arranged it to be that way (as we have for other nations in the past).
There are many factions in the US (I note on BOTH sides of the political isle) that think its worth the deficit to have China such a strong trading partner. There are various ideological reasons for this depending on which side of the isle you are on which I won’t go into here. In addition there is a large China lobby here in the US as well.
Certainly we COULD ‘lock them out’ as you say…but would it be wise? It would hurt the US’s economy and probably go a long way in destroying China’s…especially if Europe and Japan followed suit. Certainly we in the US would simply buy our goods elsewhere (though perhaps not as cheaply)…what would China do? Well, perhaps they would decide this whole capitalist thing was for the birds and go back to being hard line communists? That may not be in the US’s interests…in fact, it might be worth it for the US to have a trade deficit to PREVENT that, wouldn’t you say?
I agree that there are limits to all things, and China certainly has done much to push those limits to…well, the limit. But I think it would be unwise in the extreme to simply ‘lock them out’ for myriad reasons. It would be more wise to quietly point out the Most Favored Nation status isn’t a given to anyone perhaps. But then, I’m sure we are already doing that…
But we were talking about North Korea, no? 
-XT