If there are Christians who do not feel Mormonism falls out side of the Christian faith then they are ignorant of LDS tenets and beliefs, sadly caught up in the modern “all paths are valid”Oprah Winfrey movement in modern American Christianity and much more than likely at odds with their own faiths statements towards the LDS.
It is not fortunate that there are Christians that feel this way, indeed it is a tragedy, for in lacking the courage of their conviction they are willing to stand by as otherwise good people waltz into the gates of hell that Christians know in fact exists.
So what are you suggesting? Conversion by the sword? We can hardly send them back where they came from, now can we?
So what now? Other than castigate them daily here on FR?