Let us return to TEG for fetuses. The loss to at least some women of not carrying a fetus in their own bodies may be so great--even though with TEG this no longer means not having a genetically related child--that they would rather not have children than have them in TEG. But by not having children they will suffer a large personal cost and also prevent the existence of a new life. The violinist will be plugged into the machine if not into the man, but there will be no fetus to plug into a machine if the woman refuses the options of using a TEG or being committed to an uninterruptable pregnancy. Given these costs (no fetus, unhappy woman), should we refuse to raise the requirements of pregnancy so as to ensure the same outcome as we could achieve by using a machine?
Unless there is a shortage of children, the threat of not having a child is not very effective, especially because there is no person who is literally deprived by not being created. We therefore are left with the costs to the woman as the dominant consideration.
We need to decide in regard to machine substitutes, whether there is a morally crucial difference between pregnancy and the case of the violinist. This difference may be that once again, the standard to which parents and bearers are held when we decide what they are obligated to do for their offspring is not set by the best that would be done for the offspring by others. Why is this? Both the desire of some people to bear children in their bodies and the cost to them of not having children in this way are so significant that they compete with the interests of the fetus. This may account for the permissibility of not having to sacrifice a womb pregnancy and of our not raising the amount of risk that women must take during that pregnancy in order to match the good outcome of a machine. (What may have been left out of this discussion is the concern about who will gain control over children not bonded early on to women. If this is a dangerous prospect, there will be another reason not to hold women to the standard of the machine.)