Media coverage of this topic is complex and problematic for Mormons on many levels. I acknowledge that those not of the faith can sometimes have ambivalent feelings about it.
Why is it problematic? It is an unusual doctrine in modern Christianity and has the effect -- in news coverage -- of making Mormons appear as outsiders and secretive and weird -- as vaguely dangerous, therefore. As such, all writing on it, I believe, needs the context that it is a traditional Christian practice with scriptural support.
I would say the belief is sincere. I would suggest looking at 1 Corinthians 15:29 for evidence of this practice being scripturally based.