I suggested to my learning partner this same idea I wrote on my blog that cults are the modern idolatry.
And he mentioned a surprising support to this idea from Nachmanides. For we know strictly speaking there are very few ways of being liable for idolatry. Sacrifice, burning, pouring, bowing, service according to it way, and accepting it as ones god. So, in any case, there has to be some kind of physical object. But with the Ramban [Nachmanides] it looks like the definition of idolatry gets expanded to any being besides God, even non corporeal beings. He mentioned that when Nachmanides writes about this it seems amazingly relevant to today's issues.

At any rate, the idea that he is referring to is the idea of "Face." לא יהיה לך אלהים אחרים על פני "You shall have no other gods before me" [lit.,"before my face"].
That is the interface that God chooses to reveal himself to the world. Anything else is idolatry.
So I urge people to avoid cults, not just because of the damage that they do, but also because it might be a sin...[Enough said.]

1) My learning partner has been looking at the Nachmanides for several years and the more he looks at him the more impressed he is. There is a translation by a fellow named Chavel. Though I don't look at the Ramban at all whenever I hear something from him I am very impressed.
2) The 'Rambam and Ramban' are both actually saying the same thing: worship or praise to any being besides God is a problem. But the thing that impresses my learning partner is the coherent system of the Ramban. It  is how he shows the whole Five Books of Moses are one logical, coherent, rigorously exact system.