1 Corinthians 15:29 and Baptism for the Dead in A New Catholic Commentary on Holy Scripture

Commenting on 1 Cor 15:29 and its reference to baptism for the dead, one Catholic scholar wrote: 

Nevertheless many ancient and most modern writers understand this as a vicarious baptism received by baptized Christians on belief of deceased catechumens. The obvious difficulty is that Paul does not appear to offer any objection to this practice, so prevalent later among heretics. (John J. O’Rourke, “1 Corinthians” in Reginald C. Fuller, Leonard Johnston, and Conleth Kearns, eds. A New Catholic Commentary on Holy Scripture [London: Thomas Nelson and Sons Ltd., 1969], 1159)

In other words, the "obvious difficulty" is that Paul did not object to such a practice, though in his theology and most other theologies, such a practice would be out of place. For Latter-day Saints, however, such a practice fits perfectly with our soteriology and there is no "obvious difficulty" for us at least on this one issue.