This discussion has bothered me for a while, and I think I've just figured out what my issue is with it. (I am now going to address a bad argument that I haven't seen anyone explictly make, I just suspect that it is hanging in the air in an inchoate fashion on this issue. I may be totally off base in thinking that it's what's really going on.) There are social/political advantages to being a Christian in the US -- it's the normal, ordinary thing to be, and it means you're a traditional, decent person with family values. I think this kind of sucks. I'd like to live in a society without pressure to conform religiously, and so I'm all hardline about the separation of church and state because I don't want any additional pressure to conform religiously to come from the government.
The sense I get from the way the issue of whether Mormons are Christian gets raised is that there's a feeling that it's unjust to exclude Mormons from the privileged position of being normal decent Christian folk on narrow doctrinal grounds. And this kind of burns me: anyone who's annoyed that they aren't regarded as entitled to the privilege extended to Christians in our society should be arguing that no one should get that privilege, not trying to pass as a member of the privileged category so that they can then piss out of the tent on the atheists and Wiccans.
If Mormons call themselves Christians then I'm happy to refer to them as Christians. But as LB says, the real issue isn't whether they're Christian, it's whether they're "normal," that is, falling under the umbrella of the dominant faith tradition of the country, or "weird."
Keeping with my "people disagree about stuff" theme, I'm sure that there are those who think there are things about Mormonism which are at odds with what they consider to be Christianity. This is true about other denominations as well:
But FRC board member Albert Mohler, the president of the Southern Baptist Theological Seminary, has made several public anti-Catholic statements. During a March 22, 2000, appearance on CNN's Larry King Live, for example, Mohler asserted, "As an evangelical, I believe the Roman church is a false church and it teaches a false gospel. I believe the pope himself holds a false and unbiblical office."
Continuing on his anti-Catholic theme, Mohler wrote in a September 16, 2006, entry on his personal blog, "[T]he office [the pope] holds is an unbiblical institution based in a monarchial ministry that is incompatible with the New Testament's vision of the church. Furthermore, he claims also to be a head of state -- a situation that adds untold layers of additional confusion."
Christians disagree about what Christianity is all about, what it means, how to practice it, what institutions are appropriate manifestations of that religion, etc. Some people have very rigid views, others are more flexible, but most people presumably have a basic framework of "what Christianity is" which is at odds with other peoples' framework. Every now and then well-meaning people send me theological notes, arguing that what some religious leader said is theologically unsound or whatever. I can't referee those discussions. The point is that there is tremendous disagreement within the "faith based community" about just what it's all about. Let's stop pretending we all get along, because we don't.