For one the IC basically excludes edgier and free spirited types, or those with baggage, by design. It also excludes financially motivated people and academic types - in practice we’ve already ruled out most of the urban upper middle/upper classes and most poorer people. Among the remainder you have to pick those with college education that are willing to live in or around cities. And then among those, people willing to commit to a long career, believe in the cause, maintain discretion, unlikely to fall off the wagon… and without any kind of concerning overt bigotry. Besides people who enlisted directly out of high school I feel like Mormons are the only major group who would consistently fit the bill.
Most humans I've met are wholesome, too. Of the Mormons I've known, several are utter scoundrels, quite a few were mean and petty, and many were dishonest when it suited them. Much like the rest of humanity, there are bad people who happen to be Mormon, and good people who happen to be Mormon. Several Mormons I knew developed a drinking habit on their mission, fell out for a while, and returned to the church.
Don't buy into the mythos. They're just people. The one trait that I did note as almost-uniform among the practicing Mormons that I've known is a distinct holier-than-thou attitude. In the good ones, that seemed to keep them honest. In the bad ones, it was their justification for misbehavior -- especially the petty meanness.