It’s normal human behavior to treat individuals “in” our own self-identifiable group (be it race, religion, or culture) better than we treat people “out” of our group. This in-group preference is also normal animal behavior - which gives us some clues as to where the behavior came from, and why it’s a fairly base behavioral drive that we should strive to overcome. We live in a pluralistic society that can do without xenophobia. So here are some of my suggestions to active Mormons know someone who has left the Church (their group) feel like they are not being shunned. Shunning is also human nature, but it feels terrible to be on the receiving end.
The main problem is not the members: it's the doctrine and policy of the Church. But the doctrine doesn't exist in a vacuum; everything in life is part of a great causal web. What LDS members are taught from childhood on can obviously effect their attitudes and behavior toward “apostates” like me. However, I've observed that most members can look past the doctrinal implications and treat members like me very well. For example, my ward hasn’t done anything to make me feel "second-class." The most negative reactions have come closer to home (a perverse form of kin selection where their efforts to help actually hurt). So here are some suggestions to improve the "not so helpful" reactions that I, and others like myself, have experienced.
First, check your assumptions. One of the worst things we do as humans is infer something (wrongly) from another flimsy bit of information. For example, when someone leaves the Church, LDS people tend to assume certain things about why they left. The Church has scriptures, hymns, magazine articles, and lessons that are chock-full of assumptions about the blessed state of the faithful and the misery of apostasy. Check out the Joseph Smith and Brigham Young Priesthood & RS lesson manuals for a few characteristic examples from the normal Sunday fare. It's also just plain-old human nature to assume negative things about people who seem different than you; and nothing seems so different as when someone walks away from the Church.
LDS members usually assume we leave because of something we did (sin), or that we are running away from something (responsibility or guilt), or maybe that we were offended, or just distracted by materialism and neglected to strengthen our testimony until it slowly died out. Or maybe we were never truly converted to begin with. Whatever the assumption, it's usually disparaging to the apostate, while it simultaneously helps the LDS member cope with someone (maybe someone they trusted or respected) who left. It seems to be a cognitive defense mechanism to protect them from their own personal crisis of faith.
Maybe you know someone who left the Church who actually was a selfish, lazy, materialist who was having an affair (yes - I've been accused of this too) seemingly making the assumptions true. I’m sure the assumption is true in some cases - perhaps many. But that would not mean that it's true in every case - or even the majority of cases. Lots of people are selfish, lazy, and materialistic. The assumption was only true for the anecdotal instance you observed. Lots of people may have just wanted answers to their sincere questions and concerns - and concluded differently than you. That shouldn’t be too hard to imagine.
Instead of making assumptions, a helpful response would be to (ready for this?) ask your friend or family member why they left the Church, and then listen. I know it's crazy, but people really appreciate the openness. I know I would have. It is extremely validating and makes you feel valued as an individual. However, I can't remember anybody asking me this most basic question.
In medical school we are taught to ask people what their chief complaint is (why they visited the doctor) and then to just listen and let them talk. You discover so much about what is wrong when you can do this - and the patients appreciate it too. But doctors have this bad habit of assuming they know what's wrong after a few sentences from the patient, they quickly peg a diagnosis onto them, and then assign a treatment - all of which may be wrong because they forgot to listen. So in summary, don't assume anything, let the person speak for themselves, and listen while trying to keep an open mind.
Second, don't make religion taboo to discuss. Religion seems to be “untouchable” or “off-limits” to discuss in any context of criticism. But why should religion be afforded such special protection from inquiry - especially if it’s done with respect towards the individual believer? It's possible to critique an idea without disparaging the individual. We rationally investigate and critique the ideas of science, history, economics, politics, psychology, and philosophy (any field of knowledge in fact) and the best ideas are left standing in the end. Then why not religion? Why is it somehow off-limits? Hiding behind the defense that "it's sacred" is a cop-out; an ostrich with it's head in the sand; a wizard behind the curtain; a way to keep religion safely out-of-bounds from any inquiry.
When someone won’t talk to you about religion, then you feel shunned, and that you are less important than the idea you can’t talk about. This is my main problem with true-believing-Mormons and their allergic reaction to skeptical inquiry. Instead of silence, it would be helpful if the subject of religion could be openly talked about. Other religions, such as moderate forms of Judaism, Buddhism, and some mainline Christian churches handle debate, difference of opinion, and dialogue just fine. Unquestioning obedience to authority is something that should have died during The Enlightenment in the 18th century. I don't know why it lingers on today in the LDS church.
Also, what does it say about the strength of someone’s convictions, if they are unwilling to discuss them with someone of a different opinion? If people have really good reasons for their beliefs, then differences of opinion shouldn’t be so threatening. It seems too obvious to note that people avoid things they think are dangerous to them. That’s why we are innately scared of (and avoid) the dark, spiders, snakes, rotting corpses, heights, deep water, vegetarians, Voldemort, and midget clowns. But why is my opinion so dangerous?
Discussing different religious opinions does not have to be dangerous. I think that people (on both sides of any opinion) will only benefit when they engage in constructive dialogue. Why? Because other people usually see our faults better than we do (just ask your spouse). We have cognitive blind spots regarding our own illogical beliefs because it’s hard for our own brain to fact check itself. That’s why dictators are usually the most ignorant of people; nobody tells them they are wrong. And aren’t human beings wrong all the time about things? Of course we are; all of us; both you and me. We are humans after all - not angels! You might help smooth-off a rough edge of my beliefs, and I might return the favor. Having a certain humility of conviction, and a willingness to hear other opinions - even to change our minds sometimes - helps smooth out any dialogue.