This is an argument I see all to much.
I agree that education and resources are needed to prevent abortions.
However, natural law does not dictate that the mother should be responsible to no one for the death of her unborn child. It is not the person most affected that should decide if one option is the death of an innocent human being. This is not a private issue that only affects her; it is the destruction of a human life. However, it is also true that the person affected most is the child, who is killed. Because the child cannot speak for him-/herself; this is the government's job.
In any other situation in which one human being decides to kill another human being (we call this "homicide"), the government steps in. This is, in fact, what natural law dictates: that the government should protect human beings from each other.
As for "legislating morality", this is almost the definition of legislation. The reason we have laws against assault, murder, and rape are because these actions are immoral and violate the rights of other human beings. An action that inflicts violence upon another human being is never a private issue, and if it were the entire concept of natural rights would fall apart.
The analogy to prohibition is invalid because the consumption of alcohol does not violate anyone else's rights. The notion that a mother may harm herself in the process of killing her unborn child does not mean that the unborn child should not be given the full protection of the law demanded by basic human rights.