What is the theological significance of the label "Christian", according to evangelicals?

Recently, I have noticed a trend here of people fighting to deny self-identifying Christians who deny parts of the Nicene creed the label Christian. I am of course talking about LDS and I guess the part that is denied is consubstantiality(??). Anyway, this question is not about whether or not LDS are Christians, it's just the context of the question. Christian seems to me like a label that should be applied to those professing to follow Jesus Christ, independent of other doctrinal differences!? I found this question which deals with whether Catholics are Christians according to evangelicals , but I am not completely happy with the answers because they revolve around being born again, which is personal, as opposed to doctrinal points which seem to be the issue when you deny whole groups the label. Is there any theological significance attached to the label that causes this reluctance to grant the label Christian (according to evangelicals)? Or are there non-theological reasons?