That’s a great question, and one I’ve thought of a lot. The quick answer is yes-since Mormon “theology” and “history” is all over the place and it’s not taught very often, most Mormons, even lifelong ones, don’t have a firm grasp of their history or theology. That’s why some kids on their mission are stunned when they hear an “investigator” ask the questions about Smith Jrs polygamy, treasure digging, Book of Abraham problems, marrying 14 year olds, etc. They’ve never heard about those things, much less Kolob or the second anointing*, etc. So they don’t believe it.
The other awkward truth is that it’s very easy to become a Mormon. You show up, say that you’ve read the BOM, and then ask to get baptized. They say yes, the bishop/stake president (the SP is in charge of several wards, the bishop only one) meets them, and bam. The entire process can take as little as a month. You don’t learn very much in the process. If you did, you wouldn’t become Mormon.
The longer answer is that some Mormons actually do believe all of it hook, line and sinker. Including the truly weird beliefs like Kolob, etc. You’d be surprised how many otherwise brilliant and highly decent people believe this stuff.
*the second anointing is their “secret” ceremony where higher ups in the church get their feet washed by an apostle in the temple. They are also promised certain spiritual things, and their salvation is assured. I’ve never had it done, but if you advance high enough in their church, you can have it done.