I would say that designation of something as a cult or not a cult (in the sense in which I understand the word--as a manipulative organization brainwashing its members) has less to do with their claimed beliefs and more to do with their governmental structure and perspective of the outside world. It is entirely possible for an organization to have a benign statement of faith and yet end up drinking poisoned kool-aid. There are several considerations:
1. Does the group actively keep a "normal" statement of faith to mask their real beliefs? I have known many cults that do this. They often tell insiders that outsiders will not "understand" (because they have not been enlightened), and so it is unwise to present the entirety of their beliefs to outsiders.
2. How does the group interpret ordinary Christian phrases? Cults are notorious for giving entirely new meanings to ordinary Christian words. In the UPCI, there is much talk about "modesty." And the true Christian church would support this, right? Who can be against modesty? But then, the UPCI interprets "modesty" in a highly particular manner. A woman is "immodest" if she wears pants. She must wear skirts to be modest. She is immodest if she cuts her hair or even touches scissors to her hair. She is immodest if she wears make-up or jewelry. And then there are aberrant ideas attached to it. It is believed that angels reside in a woman's hair (totally not making this up) and that cutting her hair causes her hair to lose its angelic power. Uncut hair of a "modest woman" is believed to have healing properties and can function as the protection from disease and accidents for her husband and children. (Notice the implication here that if a woman leaves the UPCI and cuts her hair, she is a promiscuous woman who cares nothing about the safety of her family).
So you can see it took a hard left turn somewhere. But in the statement of faith, it will merely say, "We believe that women should be modest."
3. Even if a group has moderately orthodox beliefs (but most cults do eventually develop heretical ideas), I think one could still call it a cult if it was heavily abusive and manipulative and viewed everyone outside the church as evil or at least unenlightened. Even if a church claims to subscribe to the Westminster Confession, I'd still call them a cult if they declared everyone outside their particular church was insufficient in their understanding of the Confession and cut their members off from ordinary communication and fellowship with other Christians.
Isolation is a key factor in cults. They need to keep their people separated from others. They either do that physically (by building compounds in the jungle or something like that), or by declaring communication with others as dangerous and/or worldly. Generally, they will not let their members read anything or watch anything unapproved by the group, and they strongly discourage taking jobs that require a high level of interaction with the public or attending schools that are not affiliated with the group. But the best weapon at isolating their members is actually their manner of communication. You'll notice when you talk to cultists that they constantly struggle to communicate. They often refuse to use certain words. They repeat slogans over and over. They seem to be unable to understand what people say to them. Sometimes, when they are confronted with errors in their beliefs, they break off entirely and begin chanting or speaking in tongues (which they are taught to do to "block attacks of Satan on their minds.")
I think that ordinary Christians make a mistake by focusing exclusively on doctrinal errors of cults. You can't really argue these people out of their ideas. The strongest appeal, in my experience, is actually the way they treat other people. Most cultists are actually very uncomfortable with that on some level, even if they don't admit it. They may do things because they believe that it is what God requires, but it causes tremendous emotional and psychological strain. That is the weak point. And that is why most ex-cultists become ex-cultists. At some point, they said, "I can't keep hurting people like this anymore."
PS By the way, this is slightly off-topic I dearly wish that Reformed churches had more resources for ex-cultists. People are so very, very confused and disoriented when they leave cults, and they have no support network because their support network was the cult. There are treatment centers, but very expensive, which most ex-cultists can't remotely afford (having given all their money to cults). I ended up Reformed because of an email loop that helped me and suggested that I find an Orthodox Presbyterian Church. The email loop no longer exists, and most Reformed ministers, in my experience, have NO experience or training in dealing with ex-cultists. Sure, we can condemn WBC. But when those people do leave that group, where do they go?
