The entire Mexican population does not want to come to the US, so that solves that problem. If the country is going to fail, its going to be because of borrowing to pay for tax breaks issued without reducing spending, not people cleaning offices and picking fruit. The military-industrial complex is bleeding us much more than Mexicans ever could.
I would have a problem with anyone breaking into my house regardless of their color or what country they were born in. However if I chose to compensate them for providing a service that wouldn't be breaking in. Bad analogy.
Amnesty just makes sense, but not without reform to the immigration system. The problem isn't lack of enforcement, because enforcement is damn near impossible. 1986's amnesty failed not because it was a bad idea, but because the demand for immigration far exceeds the supply of legal immigration opportunities. If the REGULATION of the SUPPLY wasn't insufficient to provide for the DEMAND we wouldn't be repeating the amnesty debate. I find it interesting that conservatives don't see, or choose not to see, the free market principles at play in immigration.
And finally, but by no means less important, is that INS has been rolled into DHS and has become, in part, ICE. There is no way DHS should be given the power to create yet another secret police force; this one to track down 20 million people. Between a wall and a new DHS agency, which would likely be given extra-constitutional powers given the brief history of the agency and its crying and complaining about checks and balances from congress and the judiciary, amnesty is cheaper and less intrusive to liberty. I can see it now: DHS with the power to deport people without hearings. If you are dark skinned and go to the store without your license you might get caught in a round up and find yourself in Tijuana the same day. On top of that, we'd be paying $10,000 a month per agent to some subcontractor with waiver from the oval office on the subcontractor's obligations under the law. I'll pass.