We receive a fair amount of e-mails asking us about this subject. I can only respond by saying that a sign of a cult is when one verse is taken from the Bible and an entire doctrine is based upon it. This is a classic example of that!
Here are some articles explaining why this is biblically unsound and was merely an un-Christian practice that took place in Ancient Greece by those who were ill-informed of how God operates.
Baptism for the Dead; Why do They Do This?
Deceased Christians Baptized by Mormon Church
Unbiblical Practice of Baptism for the Dead