While rejecting the “proxy baptism” reading of the verse, Eastern Orthodox priest and scholar Stephen De Young wrote the following against the “pronoun argument” of 1 Cor 15:29
Saint Paul refers to “those
who are baptized for the dead,” meaning that he is referring to a particular
group. There are some who are baptized for the dead, and others who are
baptized, but not “for the dead.” It is important to notice that the word “baptized”
is passive in both uses in this verse. It is not “those who baptize for the
dead,” but “those who are baptized for the dead.” The action here being
described is something done by those who are being baptized, not by the
baptizer. So the fact that St. Paul refers to “those who” does not mean that is
is some other sect outside of what would be recognized as Christianity. This
verse isn’t speaking of people who perform some type of baptism other than
Christian baptism, but rather to a group of people who receive Christian
baptism in a certain way. (Stephen De Young, The Religion of the Apostles:
Orthodox Christianity in the First Century [Chesterton, Ind.: Ancient Faith
Publishing, 2021], 142)