A Potential Drawback of Mexican Immigration and How to Overcome It
One potential difference between today's immigration and that of the last wave is that today's immigration comes largely from one country. This is probably due to the fact that immigration is more easily restricted when it's by boat. I suspect that free immigration would produce more diverse immigrants.
So if you're against Mexicans (or Canadians) being an excessive percentage of the American population, you should favor more open borders.