Leaving Brighamite Mormonism typically doesn't let you keep your dignity intact, especially with close friends and family that are adherent.
At a basic level, you have to send a notarized letter to the corporation that owns the trademark "the Church of Jesus Christ of Latter-day Saints" (a virtual theocracy in Utah) demanding they remove you from their records. (cf: quitmormon.com)
At a human level, the congregations are geographically based with intense community defined within a geography and effectively-dead treatment to people outside the geography.
My parent's area has been a growth area for Utah Mormon transplants for years, so their congregation has split and moved several times. At a recent funeral for an old Boy Scout leader of mine, they remarked on how many people they hadn't seen in over a decade due to the congregation splits. I was frankly amazed -- dozens of these folks they were pointing out had been regular visitors to our home during my school years! To me it seemed strange that folks lived 10 minutes down the road, were great friends, camped together, shopped together, etc. but as soon as an imaginary line changed their friendship came to an end.
Now, when someone _willingly_ leaves Mormonism, it's often the case that their family shuns them, mistreats them, and otherwise reacts in fear and loathing, because it both signals to the intense social group that the family has failed to stay Mormon together and is a threat that makes people wonder why someone might leave. Source: personal experience, spouse experience, observed experience, reddit's mormon and exmormon subreddits.
When I left Mormonism, as a courtesy I let people know in a social media post. I received about 500 personal messages from people I knew. 90% were vilifying -- my own mother calling me "so smart it made me stupid", a uniquely East Texan insult I've come to learn -- 9% were interested, of which 8 out of 10 of those people eventually left themselves and with their families.
At the funeral I mentioned earlier, I was effectively a persona non grata. That's okay. I wasn't there for me. I was there to remember and honor a sweet man, one of the few who reached out then and later with compassion and tolerance despite not agreeing with my choice.
I believe there are a few other high-demand religions with similar institutional failings preventing freedom of thought and association, but I'll not call those out here, simply note that this isn't a unique phenomenon to Mormonism nor is it ubiquitous to religion generally.