I'm asking this in response to this question - are questions relating to scientology on topic here at mythology.SE?
Yes Scientology is on topic.
The broader topic of Will the proposed Mythology site include questions about current or major religions? was discussed during definition and the consensus at that time was
Yes, questions about modern mythology would be in scope.
"Mythology can refer either to the collected myths of a group of people—their body of stories which they tell to explain nature, history, and customs or to the study of such myths. As a collection of such stories, mythology is an important feature of every culture"
You can't define one belief system as being above questions around their mythology and still be a general mythology site.
This ties in with this meta question about drawing the line between religion and mythology. I think, discussing or asking questions about the individuals or events contained within a specific mythos/religion should be acceptable, but perhaps not questions such as "Would it be acceptable for Greeks to kill their mothers in the name of Hera?" (even though one could argue about even that).
After all, mythology and religion are closely linked. What we consider Greek/Egyptian/Teutonic mythology now was considered religion by the respective cultures at the time.
Perhaps, to ease the debate, we could draw the line at any contemporary "mainstream" belief systems, ruling out Christianity, Islam, Judaism, except where it relates to parallels between those and predating religions/mythologies?