If Americans buy only American products, how does that destroy their economy?

The
answer to the idea of how "Buy America" might hurt American economy rests in how the
interconnected nature of a globalized economy does much to reduce individual nation identity. 
This means that as manufacturing, production, and product invention and innovation have become
global elements, so much of American products are intermixed with elements from other
countries.  For example, computers that are developed in America are done so with parts from
other countries.  The interconnected nature of the globalized marketplace prevents a real strong
identification of "American" or any singular nation status.  Consider the words from
an economist, Mark Perry about this point:

"If we
restricted trade to just the 50 states, what would happen immediately -- and would increase over
time -- would be a huge reduction in our...