So Christians are supposed to "just be nice" to people who lead other's astray from God's Word and the truth about our salvation? That makes about as much sense as being too polite to tell someone the bridge ahead is washed out (None of my business, maybe it will be fine when they get there).
Yes, their disaster preparedness plans are terrific. But I'm preparing for a lot longer than the next 30 or 40 years. I'll trust in Jesus, the REAL Jesus, for my preparedness for after this very short life.
It might be helpful if they argued why you should join one of their sects and give a positive reason to switch. If all they do is downplay Mormons, then what alternative are they giving?