Drug Use and Pregnant Women, Take 2

piny of Feministe has posted an extended rebuttal of the idea that exposing a fetus to drugs in utero constitutes child abuse. Its a good response, so I'll post the meat of it in full:

If you fail to feed your child adequately, you are guilty of child abuse. If you fail to seek medical treatment for your child when your child is sick, you are guilty of child abuse. If you hurt your child, you are guilty of child abuse. If you do not supervise your child such that your child’s life is in danger, you are guilty of child abuse. When the crime is not child abuse but “fetal abuse,” however, none of the criminalized acts are things done to the fetus. They are things that the woman does to herself. If you feed yourself drugs, you are feeding drugs to a child. If you drink, you are forcing alcohol on a child.

So a pregnant woman who leaned out too far over a balcony would be guilty of endangering her child’s life. A pregnant woman who exposed herself to injury–say by working with wild animals–would be guilty of endangering her child’s life. A pregnant woman who didn’t eat well or ate too little or failed to take care of her body in any number of other ways would be guilty of endangering her child’s life. A pregnant woman who failed to seek pre-natal care would be guilty of endangering her child’s life. A pregnant woman who did not seek medical treatment for any health problem would be guilty of endangering her child’s life. A pregnant woman who refused any medical treatment or advice that might save her health or maintain her healthy pregnancy would be guilty of endangering her child’s life. She would be a criminal if she failed to safeguard her own body, and liable for any harm that might translate to her child, because there’s no difference between her body and the body belonging to her child.

The problem with this line of reasoning is that there's a fundamental difference between the scenarios discussed in the second paragraph and exposure to drugs in the womb.

Assume the following:

1. At conception a fetus is not a person.
2. At some point the fetus becomes a person.
3. An entity has the "ability to be harmed" if and only if it is a person.
4. It is wrong to harm a person; governments have the right to prevent harm to and seek redress for harm done to their citizens.

It doesn't substantively effect my argument when the fetus becomes a person; I'll assume "birth" for convenience.

Assuming agreement with assumptions 1 through 3 then there's not an issue with the scenarios in the second paragraph. The fetus is not a person, so putting it at immediate risk does not warrant government scrutiny. The person that the fetus will become is not materially affected by these actions, so there is no reason for government intervention on that account either.

Contrast this to the drug use scenario. The damage inflicted by drug use persists past the point (wherever you define it) when the fetus becomes a person. At that point the now-person has suffered harm as a direct result of the mother's actions in the past. Provided agreement with items 2 through 4 the government has a legitimate interest in preventing this situation and seeking redress when it does occur.

Rebuttals?