Okay, I was in the LDS church and yes, it is a cult.
Why has it gained acceptance?
They've worked very hard over the last 15/20 years to make themselves acceptable. They have started using terms familiar to Christians and have strongly pushed to put themselves in the public eye as a Christian denomination. When one first joins, they are not made fully aware of all the beliefs and discourage members from studying on their own, claiming that newcomers must have "milk before meat." Even those who grew up in that system of faith often remain woefully ignorant of the complete history and full beliefs of the LDS church.
An example is the Bible. No missionary will come to your door and say "we don't believe the Bible is true." They claim to use the same Bible, and indeed they do. Later you find they believe it contains major errors and that only the writings of the prophets and/or the "fixed" version of the Bible Joseph Smith wrote, which conveniently contains a prophecy of his own coming. So it must be true, he wrote it into the Bible and said it was supposed to be there before, but it was lost because the fullness of prophecy was taken away from us for a time but glory be, it is BACK!
Another example is that they don't advertise that they don't believe Jesus is who he said he was. He's just another one of us...God's spirit children, as is Satan, and his blood was only shed for us AFTER all we can do. His blood alone is not enough. He isn't the key to heaven for those in our time, Joseph Smith is the prophet for our time and holds the keys to heaven, so you can't get in without his permission.
There's so much they don't say. It sounds like a typical Christian presentation based on Christian doctrine.
They're also very family oriented and that is very attractive. They got things right on this part...they do take care of their own and people work together. It's the way things should be. They act like Christian should act but don't when it comes to their emphasis on family, health, and taking care of the poor, elderly, or sick among them.
So why wouldn't they gain a rapid audience? They sound good. They look good. They're powerful. They make one feel safe. They make one feel loved. They make one feel cared about.
It FEELS right and it LOOKS right. Unfortunately, the end of it is death, eternal separation from the Father because they reject the truth. They reject the power of the cross, they reject who God is, they reject who Christ is, and that means that no matter what they say, they reject the one and only true way of salvation. They still believe we are in need of priest, and don't realize that with Christ's death and resurrection, we no longer need to go through a priest. If there's anything you try to drill into a missionaries head before you get black-listed, make it that - we have no need of an earthly priest anymore, we're all on level ground now and anyone claiming otherwise is a liar and those believing it are deceived.