I was specifically referring to the Calvinist belief that Christ's grace alone provides salvation to the pre-destined, whom are "unconditionally elected", i.e., chosen for a fixed salvation regardless of their past or future conduct. While stating this theological difference, I recognize that many Calvinists believe that living a conforming Christian life is a necessary signal of this election.
As it pertains to the topic at hand, the point was to illustrate that mainstream Christians are less likely to be concerned over changes in affiliation, or even some changes in conduct, due to this doctrine that the "priesthood of all believers" is active and allows good people to re-affiliate freely. Combined with the Calvinist doctrine of unconditional election, which is widely but not universally accepted in mainstream Protestantism, specific religious distinctions are of little concern to many Protestants.
I was more concerned about the more popular misconception about protestant Christianity: that it mostly involves claiming a label then going to heaven. This does a lot of harm because a lot of "Christians" are more or less untrained, unaccountable, and frankly bad people. And they are the examples often brought up when discussing hard feelings and distaste for Christianity.
I'd also wouldn't blame predestination for the lack of stress on membership and the consequential toothlessness of shunning. It more has to do with the removal of actual priests (i.e., with collars and robes) from any sort of essential role. You don't have to make any particular clergyman or bishop happy to have a birth blessed, a holy funeral, an honorable wedding, or salvation itself.
That's not what that means to a non-Mormon Christian. In fact, as far as behavior goes, it calls for the opposite. Reading 1 Peter chapter 2, it's clear that it says that Christians are all responsible for priestly duties, in the way they behave, the way they speak, and the way they care for the spiritual lives of the people around them.
Even more clearly, at the end of James 2, it says exactly the opposite. It says trust in God is empty if your trust isn't influencing your behavior (faith without works is dead).
The notion of a priesthood of believers is significant in a way that contrasts with the Mormon church, though. Protestant Christians believe that the healthy Christian Church enables and supports Christians (and everyone else for that matter) but that no organizational leadership functions as gatekeepers "the saved", godly marriage, or any other special status.