The similarities between immigration and international trade have led some to conclude that they are roughly equivalent. However, while they are alike in many ways, there are also a number of important differences that are often overlooked by immigration enthusiasts. Both alter the supply of labor, for instance, but while trade does so implicitly for only so long as goods are imported, immigration does so permanently.
Immigrants also consume public services.
What's more, immigrants are human beings, and have rights which cannot be ignored when economically convenient. Because these differences are at least as important as the similarities, both need to be considered when formulating a sensible immigration policy.