I see this as two separate issues... One being the tragic and senseless murder of a boy. The other, was a discussion of different belief systems/religions.
Name calling is counter-productive IMO. If you fall on one side of the discussion, fine. Put your points on the table and others will discuss it, pro and con. Simple as that.
My points on the table...
1- Posting religious propaganda on a post related to a murdered Mormon is
a-inappropriate
b- insensitive
c- unChristlike
2- see point 1
Discuss...
Simple as that.