3. Almost all of the European countries have too low birth rates, not just Italy. Germany's fertility rate is 1.4, and their economy is one of the strongest in the world. And btw, Italy's is also 1.4. So maybe the problem lies elsewhere?
As for who immigrates to the US, have you looked at the names on research papers and technology companies and hospital doctor lists? Half of them are not americanized names. We've been sucking the brains out of the rest of the world since WWII. Unfortunately, we do seem to be changing immigration policy to change that. Also, the children of immigrants are the main driving force in our economy; they are the ones who get the advanced degrees, and start the companies.