That's because their anti-free trade agenda is of a piece with their socialism. It goes like this: Big Oil is evil and out for itself, Big Tobacco is evil and out for itself, Big Agriculture is evil and out for itself...
...Big government is good and only cares about the little guy.
That's why it's not some cosmic coincidence that Ralph Nader is against free trade while Rush Limbaugh and William F. Buckley are for it. That's why even Pat Buchanan would admit he believes in free markets only up to a point.
Look, being against elements of NAFTA or any other trade agreement is one thing. But if you think that higher tariffs and duties in and of themselves bring greater proseprity, you'll have to explain why Hong Kong has been so prosperous all these decades without either.