The Amish and Hassids live apart from mainstream society, but have regular/daily interaction. The Amish through tourism and the Hassids through commerce. Both also maintain the classic family structure.
For the record, there is a surprisingly large population of Mormons in NYC -- both practicing and non-practicing.
OK, let's take it to the next step. Let's assume there is a religious group that does strictly isolate its members from society because they believe that is what God wishes them to do.
How do we know they are wrong about God's intentions, other than by essentially saying "their religion is false, and mine is true"?
The Amish really do not like or promote the heavy tourism of people gawking at them in places like Lancaster County, and they don't have anything to do with a lot of the touristy "see Amish life" places and shops on the main roads; some make and sell furniture off the beaten path, some of it to tourists, but almost no actual Amish really make their living off tourism.
But they're primarily farmers and they'd be quite pleased, I suspect, if another tourist never set foot in Lancaster County. And they're not really all that cut off from day-to-day society. You'll see them in stores, taking fishing charters in the ocean or fishing off piers in Delaware (which they're really big on for some reason).
How are the Mormons more separate from society than Amish or Hassids????
I mean, if a Mormon is the governor of the state of Massachusetts, that's about as involved in society as you can get.
Apropos our discussion of cults, here's an article from today's paper regarding Scientology and Tom Cruise. Some interesting details:
http://www.latimes.com/business/la-fi-scientology18dec18,0,2963052.story?coll=la-home-headlines