I'm sorry, but letting them have instate tuition (which is not FREE) is not an incentive, it's a deterrant. Only very, very few quality and they must be pursuing a legal path (yes we do have a number of legal slots for immigrants including those from Mexico that are for people with a higher education and skill level)
The legal path is such a pain in the ass that the illegal route has become the path du jour simply because of its ease. Illegals should not be receiving ANY government subsidies whatsoever, in-state tuition included. You can't reform immigration policy by allowing exceptions. I am sick of my tax dollars subsidizing illegals when many of our own kids can't afford a decent education. Americans first...