I think the problem is that a true believer can acknowledge that it behaves like a cult, but still believe that it is "truth." I was somewhat in this category for a while - sitting at the KH listening to a talk about shunning apostates or not accepting literature from someone even if it meant they'd read yours, or listening to all the loaded language - I thought to myself "If I were creating a cult, that would be something I would do." That didn't mean it wasn't "the truth" to me though. I just thought that god wanted to run his organization like a cult. If that was god's way of doing things, and I was gonna get to paradise out of the deal, who am I to argue?
I think the key here is to introduce a couple concepts over time and let them come together. You need more than to think/know that it is or might be a cult. You then need to have some reason to doubt the efficacy of the doctrine - something significant enough that the idea that it's a cult allows you to realize that you might've been fooled and understand why. One of the big factors that keeps people trapped in a cult is the idea that they're smart and don't think someone could have fooled them. If someone understands that anyone could potentially be fooled by a cult, they're much more likely to be able to accept the possibility that they've been fooled and that opens the door to a more objective explanation of failed prophecy, extra-biblical rules, and flawed doctrine.
When I finally came clean to my wife about wanting to leave I called it a cult rather openly and she asked me "well if you think they do all these things that make it a cult - what would you have them change to not be a cult?" I realize in retrospect that her question was rhetorical - she was saying that even if it was a cult, or behaved like one, it couldn't be changed because that's how god wanted it.