Even the current proposed bill, which requires many of them to return home for one year before coming back, would fall short of your standards. "How can we expect them all to do it?"
The answer is that the current crop of illegals were not herded up and moved here at gunpoint. They smuggled themselves in, often at great cost and risk.
So merely trudling over to an ICE office for voluntary, safe deportation (with air conditioned offices, and meals en route, no doubt) is a snap compared to coming here.
Nice try, though.