Thompson is wrong because she ignores the existence of positive moral obligations. She concedes personhood to the unborn because she has to for the rest of her argument to make sense, but then sets up a system where you could argue that parents have NO obligation to their children whatsoever.

We are used to discussing moral obligations in the negative, ie I am obligated NOT to bash your brains in. Positive moral obligations also exist. In fact, agreement is pretty universal in regard to a parent's positive obligation to care for their offspring. If you leave your child to die from exposure, the State will punish you. Given that Hamiliton has already conceded "fetal personhood" and that a fetus is located in its natural environment, it is reasonable to argue that the mother has a positive moral obligation to provide support. Consent, autonomy, and the rest of such dreck are dishonest distractions.