Mormonism deeply values work ethic and breeds a strong trust of authority.
You're taught at an early age questioning authority is a sin and doing what your leaders tell you is the right thing to do.
The end result is a group of people who are hard working, don't question leadership, and do what they are told.
If you aren't allowed to question leadership and are instead expected to do "what you are told", then all the experiments and horrors studies on group think are a reality at a dangerous level [1][2][3] What if you think an order is dangerous and have good reasons why?
Good leadership needs to know what the ground-level knows, they need good input and questioning. Stalin killed anyone who opposed or questioned him, so all of the input and feedback was only positive feedback/intel to avoid being killed. Even when they were setting up one of the worst famines in recorded history [4].
Healthy societies aren't cults, and that is definitely a description of a cult.
I hate a Godwin-Law argument, but the damn Nazi's "did what they were told" [5], and those 'hard-working'-don't-question-leadership lemmings had a blind-eye to/assisted and/or murdered millions of people because they didn't have to deal with the burden of questioning and thinking for themselves. Fuck that.
[1] https://en.wikipedia.org/wiki/Stanford_prison_experiment
[2] https://www.prisonexp.org/
[3] https://en.wikipedia.org/wiki/Jonestown#Deaths_in_Jonestown
[4] https://en.wikipedia.org/wiki/Soviet_famine_of_1930%E2%80%93...
[5] https://www.pbs.org/newshour/science/how-the-nazis-defense-o...
We know what group-think does way beyond the experiment. We have a very well-documented history on it. Read Soviet and Nazi history, you'll see what it can do. It's almost universal in big groups of humans.
If a police officer told you to shoot another person, would you do it? If 3 police officers tell you to do it, would you do it? How many police officers will it take to make you shoot the person?
Has been throughout history!
I agree it's not "spreading" per se, but their numbers are respectable among proselytizing religions today. When Islam reached a 1.8% growth rate in the 2000s we were inundated with proclamations that it was the fastest growing religion in the world (eg: https://foreignpolicy.com/2007/05/14/the-list-the-worlds-fas...).
This article from 10 years ago reports that 56% of Mormon live outside the US and Canada at that time- https://www.deseret.com/2013/8/30/20524833/the-majority-of-m...
Mormon membership numbers of actual adherents are likely 20% to 40% of membership claimed based on "inactivity" rates (and people leaving).
Samoa is a big one I guess.