One of the common arguments against protectionism is that America should not be trying to hold on to manufacturing jobs that are going overseas. The idea is that we don't really want the shitty manufacturing jobs anymore; we're going to stimulate the economy through innovation. We should be building new jobs that no one else has ever had before. Forget the old jobs.
But, is the fruit of innovation enough to sustain employment? A breakthrough like the world wide web doesn't come very often. Plus with every successful idea, there are many failures in between. If we're trying to sustain our economy through innovation without protecting existing backbones of the economy, such as manufacturing, we're going to go bankrupted.