I do think some of them honestly believe they died and went to heaven/hell, so they feel strongly motivated to share what they have "learned."
Can things like that be debunked? Yes and no. You can examine certain features of the experiences that would indicate they are more similar to hallucinatory sleep experiences, for example, than actual out-of-body events. There are interesting cross-cultural studies of NDEs that seem to indicate that what people see in an NDE is largely culturally dictated. You might find this article interesting:
http://www.infidels.org/library/modern/keith_augustine/HNDEs.html
