I have had up-close, prolonged exposure to two such groups in my life so far, first when my then-stepmother converted to Mormonism when I was a teenager/early 20s, then later when my father converted to the Iglesia Ni Cristo (a weird sort of Mormon/LDS-imitating religion from the Philippines; he wanted to marry one of their members, so he had to convert to do so). From what I saw, the issue is not so much that they presented themselves as the true Christians (so does the Roman Catholic Church, so does Eastern Orthodoxy, so does Oriental Orthodoxy, etc. -- churches that very rarely get called 'cults', and are very long established, so they don't qualify as 'New Religious Movements', either), but that since they argued their incredibly weird beliefs using various Bible passages, they were able to accepted by people who don't know any better, like my father. One day I remember him saying to me "I can't believe how Bible-based the (INC) church is! It's amazing! I read the Bible, and everything they say is in there!" I told him "Yes; that's how Christianity-based cults work." (By this time, I was an adult and had no trouble nor anything to fear from talking to my father this way.) He didn't really understand my point, but just got mad at the use of the word cult, even though I swear to you this group had a little card that they stamped to show that he had attended X meetings in a row, which was a requirement for his baptism into the group. It was like one of those "Subway Sandwich Club" type-cards that used to be a thing years ago where if you bought X number sandwiches, you could get a free sandwich once every necessary visit was recorded on the card. Except instead of a sandwich, he got baptized into this incredibly heretical and weird group. Honestly, he would've been better off with a sandwich instead.
This probably won't win me friends among many Protestants (I don't know about present company), but I do believe that it should be taken as more or less an unofficial rule that the Bible, in the hands of an idiot, a delusional person, or a shyster, has the capacity to be far more dangerous than beneficial. Reading the scriptures requires understanding which must be learned (see, e.g., Acts 8:31), precisely because without some fundamental understanding to ground a given reading (whether that understanding comes from a Protestant, Catholic, Orthodox, or even Nestorian tradition...at least these are extant faith traditions, even if they don't all agree on everything), it is possible to argue for or against anything, or to claim to prove any principle, using the scriptures, and many people are blinded by that.
I mean, Creflo Dollar is a minister, for Pete's sake. I have a friend who became a minister online for the purposes of officiating his friend's (secular/non-religious) wedding, and it was apparently accepted by the state of California, where the couple were legally married. These days at least, being able to read the Bible and take away this or that idea from it simply means you're literate, not that you're 'Bible-based' in any way beyond "these particular words are found in the Bible" (as though there is no interpretation whatsoever involved...I always wonder how these extremely individualistic, 'Bible-only' churches tackle difficult books, such as St. John's Revelation or the Song of Solomon...I have seen Islamic rants against Christianity that use the Song of Solomon as evidence that the Bible is "full of inappropriate contentography", which...yeah, I'm not going to lie, I could see how someone who read it without knowing what they were doing could get that impression, given how graphic some parts are).