It really makes me sad. I have a few people very near to me who are faithful to the church. I don’t want to destroy their faith, because it would destroy them, so I shut my mouth, but I still feel bad.
I know it is hard, but it akin to telling an alcoholic they are drinking themselves to death.
The Bible says without Truth we are already perishing. Every parent who loves their child will tell them not to walk into traffic. Yet, we hesitate to tell God's creation not to believe a lie.
I have thought a lot about that. I believe God does that when people reject him over and over. He probably finally says something like: "Fine - if that's the way you want it, you have it that way, but know this - it has consequences."
The key idea is to transfer their faith -- from Joseph Smith to the true Jesus Christ. Any faith in a mere man is a sandy foundation. (There's a Sandy, Utah for a reason)
This is true ONLY for a very few.
As my military drill sergeant crushed the wills of many men; only to rebuild them in the manner needed, Jesus Christ can take that 'broken' soul and make it into one of His followers.
In fact; if a person is NOT 'broken', there is no need for the Master to heal them.
Your concerns regarding their response to finding out that mormonism are justified in part. Mormons are so ingrained on the notion that everything outside of mormonism is false, that when many of them leave the mormon church, they reject ALL religion (kinda a mormon scorched earth policy) and become atheists/agnostics. However, just like trying to warn the driver of a car that the bridge ahead is washed out, one must still try. It seems that one of the key aspects is a personal relationship with Jesus Christ. If they can be 'anchored' or assured of that, it will keep them from being destroyed when they see the rest of mormonism fall down around them.