It's all about paying low wages. The whole thing about an illegal having a child on American soil automatically makes them both legal is just a loophole. Politicians say it would be inhuman and just plain mean to separate a child from their mother, but true Americans know it's all a ploy, because big business bastards love to immigrants, because they're stupid and will work for close to nothing, and their kids are going to be stupid and work for close to nothing, as well.
But nobody gets deported, anyway, so this law is pretty unnecessary, now that I think of it, because deporting people is mean, too, and we don't want to mean, because being mean is wrong, and nobody is going to like a nation of mean people.
When you really look at the logic of the law it is so obviously flawed. The baby was born on American soil, so what? It came from a mother, who is illegal. Therefore that parental bond means that the baby should be illegal, too. Would it be so inhuman to send them back to their own country?
In Spain, it is legal to deport illegals in straightjackets, and they have none of this nonsense about an illegal's baby being a legal citizen. In the US we won't even touch our illegals, instead, we give them driver's licenses, welfare and jobs!