Just to be accurate, 67% of Republican Congressmen voted for China MFN while only 51% of Democrats this. This is not to say Democrats are angels, but that the fact of the matter is that Republicans from Nixon to Bush Jr. have been pro-China trade. It was Bush Jr. who signed off on China joining the WTO and thereby gave China permanent MFN status. The only difference between Clinton and Republicans on China may be that whereas China had to allegedly bribe Clinton to be pro-China trade, the Republicans all voted for China trade completely and absolutely voluntarily. As for "slave labor," Chinese dissident Harry Wu has said that there's about 8 mil. Chinese in laogai prisons at any given time. This is a small percentage of China's overall population. It's true that China has cheap labor but this cheap labor is not necessarily slave labor but just regular average workers who don't happen to make a lot of money by First World standards.
As for China's labor policies, what they classify as volitional labor, would be considered in most civilized societies as abject servitude as I have personally known quite a few Chinese whose vocational paths had been predetermined by government assessment committees and assignments according to their "ability". Furthermore, Harry Wu's revelations were but a tip of the iceberg of subject labor, prison labor, child labor, and labor as penalty (not including prison labor proper). Yet even this isn't really the crux of the issue. Our national industrial base is, and wildly one-sided trade with this one nation to our detriment is the issue. That not only equals a dangerous trade dependency with China, but an undeserved enrichment of a totalitarian society at the expense of other more rational and democratic ones including our trusted and proven allies. We don't need to feed a shark waiting to bite our heads off at the first opportunity.