You just cannot win over immigration reform advocates by saying that you'll try to tinker at the margins with your enforcement-oriented immigration policy. From the L.A. Times:
Administration officials say the goal is to focus enforcement on deporting people who have committed crimes. But the effort also has a political context. Obama has been criticized by Latino activists for deporting a record number of illegal immigrants even as the president has publicly called for reforms. With Congress unwilling to approve immigration legislation, administration officials have been looking for actions they can take on their own.