One of my favorite things is to watch dramas set in Tudor England, and hear my sect of Christianity referred to as "The Lutheran Heresy". It's cute and archaic, until you learn that some sects of Christianity still refer to Lutheranism as a cult or heresy, and it's the 21st century. It's downright uncomfortable if the way you learn about this is because you are dating a man whose mother is a member of that sect who thinks you are a damned Jezebel for your blasphemous ideas that babies can be baptized and women are allowed to sit with men in church.
When Robert Jeffress mentioned that Mitt Romney was in a cult, it really didn't bother me, mainly because I have a feeling that Robert Jeffress would refer to anything other than MegaChurch Southern Baptist as a cult. What I find dangerous is that anyone would take this man seriously and not vote for someone because his religion is inferior to that of Rev. Jeffress. So, no, I personally do not think that Mormonism is a form of Christianity - it's close and shares a lot of the same history and ideas, but there's enough of a difference in the basic tenets of the religion that I could not see them as being the same. It's like Islam and Christianity - lock step until the Crucifixion, and then they diverge substantially.
That doesn't mean anything. Everyone is entitled to believe what they would like when it comes to religion. Just being an adherent of one sect or another does not make you a good person or not. What makes you a good person is in your words, actions, and how you treat others. Bad people can still go to church and call themselves Christians - just look at Rev. Jeffress.