They don't have enough of a middle class to be a viable market for US products. We have no real reason to have granted them Most Favored Nation status, which should have been reserved for countries that buy from us about as much as we buy from them
Once we allowed them to join the WTO, we had no choice since that is part of being a member.
Assuming you mean within 50% (meaning 0.67 to 1.5 ratios of exports to imports), that list would be:
Pretty empty list there... In actuality, according to the CIA Factbook, we exported $50 billion worth of goods to China in 2006, and we imported $220 billion.
Japan? Exported $50 billion, imported $180 billion.
Mexico? Exported $120 billion, imported $180 billion.
Canada? Exported $220 billion, imported $350 billion.
Germany? Exported $40 billion, imported $75 billion.
So based upon the above, we shouldn't have MFN with anyone. Heck, China's about on par with Japan in terms of exports/imports, so neither should get MFN?
We don't have parity with any country - we're a net consumer of durable goods, compared to everyone. But we're still the largest exporter on the planet, equalling the entire EU in terms of exports. And our economy accounts for a quarter of the entire world.
MFN trade status should be used to our advantage - when we can maximize what we get for our dollars. Restricting trade to countries closer to parity - Germany, Canada - means we can buy more expensive goods, tools, and services which will hamper our own economy more than letting businesses get their supplies/products at the lowest cost.