They are lovely people. I've met some. They do seem to have a very strict religion AND a strict church to go with it. (See Jim Beverley thread- churches and religions go together but aren't the same things).
The thing is this: if a person asks for permission to do things- even if those things are matters he doesn't need anyone's permission to accomplish or execute- the people whom he's asking will always grant it, instead of saying "oh, you don't need to ask permission." IOW, give others power, and they'll take it.
The problem with LDS is a problem that's common to cults - there's invasion in members' lives.
The reason groups like that are considered cults and not mainstream churches is that mainstream churches (or elder churches, if you like) have mostly become far more user friendly. There are exceptions like Orthodox Jews, some Protestant sects, radical Islam, yes, but in the main, organized religion has moved forward greatly in the past couple hundred years.
I think LDS has, too, from what I've read, though they are still strict. Groups like the FLDS sects are truly cults. They are different. They are a step back into fundamentalism and outlawed practices and some of them have been linked to murder and other crimes.