By most definitions, a cult is a religious group that demands absolute allegiance and obedience to a charismatic leader, and that discourages or outright disallows contact with others outside the group, including family members. That covers the People'e Temple, Aum Shinrikyo, the Branch Davidians, Heaven's Gate, and any other group I can think of that is by consensus considered a cult. Mormons do not fit that definition.
I've seen a lot of Christian groups that define a "cult" as any group of individuals that do not follow orthodox -- for their own definition of orthodox -- Christian teaching. According to those folks, Buddhism is a cult. The book you endorsed, based on the Amazon summary, endorses that view. That cheapens the word "cult" by reducing it to "any groups whose beliefs aren't mine, or reasonably close to."
You said — “I’ve seen a lot of Christian groups that define a “cult” as any group of individuals that do not follow orthodox — for their own definition of orthodox — Christian teaching.”
That’s exactly the definition — in terms of “Christianity”. I thought I was in the “context” of Christianity. If I didn’t specify that, first — then I should have clarified that the context *is* Christianity. And thus, the *definition* of “cult” is according to a Christian definition.
That book — Kingdom of the Cults — is a Christian book because it compare the *essence* of Christianity (what the basics are) across the board with all the other groups around. It’s a tool for Christians to be able to define and identify those (other groups) who *deny the faith* — by *rejecting* one or several of the basic, historic and foundational doctrines by which *all* must adhere to, in order to be called “Christian”.
It is a definition for Christians in order to maintain the faith of Christianity — as something *different* and *apart* from all who are *non-Christian*.
It’s not a narrow definition — but quite wide-based and covers many many Christian groups and denominations. It serves to let anyone know who is *not Christian* (in their teachings and doctrines in that they deny certain basic, historic and foundational doctrines of Christianity).
Regards,
Star Traveler