Only because we made the "overstaying" an illegal offense. But there's no reason to -- if the guy was paying taxes the whole time, and never committed a serious crime, then we should be happy to welcome such guys, ramping up our GDP.
Don't forget that the paperwork costs a lot, if one has children, can get close to $10k.
Look at Spain -- instead of deporting "illegals", they just made them "legals" (those without a criminal record). Easy, problem solved.
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If he was paying taxes during that time period he was also committing a felony.
You make it sound like deportations happen because of some mistaken legal wording. That's distortion of reality. A significant amount of US citizens voted for them to happen. I'm sure they heard about GDP many times and still found other reasons more important. It wouldn't be a wild guess to assume that they won't buy Spain as a good example.