"Even if the thirteenth amendment provides textual support for Roe’s holding, what, if anything, has it to say about the jurisprudence of the abortion cases that followed Roe? To begin with, there is one kind of case in which the thirteenth amendment argument is simply overpowering. A demand by the father that the pregnancy continue, however deeply he might desire to procreate, would be a request that another person’s body be placed at his disposal for his purposes. A law giving the gather of the fetus the right to veto an abortion would represent the easiest thirteenth amendment case of all."