Discontented people within your borders are a much bigger problem then discontented people outside your borders though.
Also, as a potential future immigrant (native English speaker, doing a PhD in the US, not very culturally distant from Americans except perhaps for a greater appreciation of Monty Python) I would feel extremely alienated if told I had to pay higher taxes for the rest of my life just because I was born elsewhere. The current immigration system may be frustrating at times, but at least I can hold onto the hope that if I become a citizen here, I will have the same rights as everyone else. (Except running for president, which isn't relevant to my planned career path anyway.)
