Wealth cannot be created in a closed system. Isolationism and protectionism do nothing to increase the wealth of a nation. If anything, they destroy that wealth.
How is it that you think wealth is generated, if not by increasing the flow of money into an economy?
In a closed economy, you have fixed wealth. The only thing that ever changes is who has what portion of that wealth. Our need for imports, however, will not be lessened. We will continue to import quite a bit. The trade deficit is harmful to our economy and harmful to our wealth as a nation.
The trade deficit is the real problem here, and protectionism and isolationism do nothing to resolve it.
I mean, really...just ask China how well their closed economy worked.