I'm all for separation of church and state first off, get that out of the way.

The issue of LDS really being Christian is a different thing entirely. The other denominations you mentioned have differences in doctrine, sometimes major, but have a common thread in some interpretation of the same bible. 

While the Mormons claim the bible, their true doctrine is in the book of Mormon and in on going revelations from their prophets. 

They use the word Christian, but the God they worship is a man become god. Their goal is to become a god in the same way they say he did.  Ultimately each "saint" hopes to have his own planet surrounded by his wives and progeny. 

Instead of being a different interpretation of the bible, the book or Mormon states that you are a fool to believe that all you need is the bible. 

Grabbing a bible, naming your group "christian", then creating your own doctrine doesn't make you christian. No matter what underwear you wear or how polite your kids are.