Steven Camarota writes at National Review on why Heritage gets the most important details right:
Probably the main argument of critics is that the economic benefits we gain from having access to immigrant labor will offset the fiscal costs. There is simply no evidence for this. The National Research Council study mentioned above, which was authored by many of the leading economists in the field, is the only study of which I am aware that tried to measure both the economic impact and the fiscal impact of all immigrants. That study found that the economic gain to the native-born from all immigrants was smaller than the fiscal drain created by all immigrant households. And that finding was for all immigrants, not only illegal immigrants, who have on average just ten years of schooling.