It is true what you say that Mormonism has grown fairly rapidly.  Success does not equal truth.  You should not be deceived by the American philosophy that success in the eyes of the world implies "good" or "truth."   Islam has grown rapidly, but that does not mean it is true.  For a long time Communist philosophy grew rapidly as well, but atheistic Communism is definitely not truth.  By this standard, Microsoft is truth.  Satan is perfectly happy if the Mormons are successful.  The Bible says that God will allow people to accept a powerful delusion.  Scriptures which are relevant to Mormonism include 2 Thessalonians 2:1-4 and 2 Thessalonians 2:9-11. 

Do Mormons do good things?  Yes they do.  Buddhists and Atheists do good things as well.  This does not mean that they teach the truth or that they are saved.  Do not be deceived by outward appearances.  Paul said in Galatians 1:6-9 that if someone preaches a different gospel than that preached by the apostles, "let him be eternally condemned."  These are strong words, but they are the word of God.  Mormonism teaches that we are all gods and that we can all be God like the God who created Adam.  Joseph Smith said that Jesus was persecuted and killed because he took more than one wife.  Such lies cannot be accepted.  It is true that in many ways Mormons appear to be good Christians, but the teachings of Joseph Smith are satanic, not from God.  I urge you to check these rather strong statements for yourself (including the power point and outline at my web site as I mentioned earlier).

John Oakes