Baptism by proxy
The physical nature of the baptisms for the dead is also appealing to me. I don't remember my own baptism, so the only memory I can refer back to is the experience of being baptized for other people. The jacuzzi-temperature water and fancy baptistery of the temple are probably more pleasant than the circumstances of my actual baptism anyway.
With the billions of people who have lived and died without a trace (and continue to do so), I don't think we're making much of a dent in the work to be done. And I think it would be petty to complain about the massive amounts of duplication and ambiguity in the work that we actually do (I remember being baptized for 6 guys named Wolfgang, with no last name). For these reasons, I think these baptisms are for the living, not the dead. For me, that's good enough.