That isn't. It's not rewarding the parents for their crime. The child being born is still born either way. The child doesn't need to be a citizen of the United States regardless of the citizenship of the parents. In this case, the parents being foreigners deliberately set out to have their child in the US in contravention of US immigration law with the knowing intent the child would become a US citizen and that would confer benefits and advantages to the parents.
If the child weren't to become a US citizen, the child would still be a citizen of the nation the parents were from so there's no loss there to the child. It isn't as if the child chose where to be born.
Your argument is the child having been born in the US, by no action of its own, is harmed by not being made a citizen. That's absurd. The child isn't harmed by not being made a citizen. The parents retain responsibility, and the parents gain no benefit from the child's place of birth which is THE ONLY REASON THEY KNOWINGLY CHOSE TO HAVE THE CHILD IN THE US! That is, the parents are the one benefiting from their crime.