Justice vs. Mercy in Immigration

Currently, welfare programs in the U.S. are being used by a large number of illegal immigrants. How does the Word of God speak to immigration, and what should be the balance between justice and mercy? Liberals prefer to ignore the fact that sin is everywhere, and choose to believe that all humans are basically good. However, to do this is to consign the world to chaos. What is our personal responsibility, and what is the government's responsibility, when it comes to this issue of illegal immigration?