From the outside, it's easy for me to label people "Christians" simply by checking whether they place Jesus Christ as more important than any other holy figure.
But nobody owns who is and is not a "Christian" (except God, of course), so I really can't tell people they have to accept Mormons or Cahtolics as "Christians." Everyone has a right to believe in whatever they chose, and that includes believing who is and is not a coreligionist.
Why are Catholics constantly singled out as being "less Christian" than many other Christian sects? They came first, have been around the longest. Not saying that faith is any better than any other, but it strikes me as odd. Also, by my understanding, several Protestant faiths do not believe in a heaven or a hell, so the "eternal life" argument doesn't really work as a basis of being Christian.
Christianity rests in the belief in Christ's teachings, not belief he was the son of God or anything like that.