And the very next verse reads
"And as for us, why do we endanger ourselves every hour?"
Note that Paul makes a distinction between "they" and "we".
But the objections to this interpretation are obvious:
(a) There is no evidence that such a custom prevailed in the time of Paul.
(b) It cannot be believed that Paul would give countenance to a custom so senseless and so contrary to the Scripture, or that he would make it the foundation of a solemn argument.
(c) It does not accord with the strain and purpose of his argument. If this custom had been referred to, his design would have led him to say, What will become of them for whom others have been baptized? Are we to believe that they have perished?
(d) It is far more probable that the custom referred to in this opinion arose from an erroneous interpretation of this passage of Scripture, than that it existed in the time of Paul.
Paul is arguing FOR bodily Resurrection which means the Corinthians were arguing against it. If the Corinthians are practicing baptism of the dead, what is the point if there is no Resurrection of the body?