Selective terminations and respect for the disabled

It is widely thought that abortion on the grounds of fetal abnormality is morally justified. More controversially, Peter Singer has argued that some infants with severe disabilities ought to be killed. Many disability rights activists object that such claims and practices express disrespect toward disabled persons, even if fetuses and infants are only potentially persons. This can seem puzzling. If disabled fetuses are not members of the community of disabled persons, how can our treatment of the former express disrespect toward the latter? In what follows, I shall argue for two claims: first, the he puzzle is only apparent because whether we respect someone depends not only on how we do treat him but also on how we would treat him were circumstances different, and secondly, "substitutionary arguments" for selective terminations of disabled fetuses or infants do express disrespect toward disabled persons, even if fetuses and infants are only potentially persons.