The basis of Mormonism is no more illegitimate than the basis of any relgion

[The Mikado]

the bible was written by dozens of people over many centuries - yet it is very deep and entirely cohesive.  

Entirely cohesive?

The Bible contradicts itself and gives contradictory messages all over the place.

You lot have just developed a very convoluted way of thinking to reconcile ''Thou shall not kill'' with all the slaughter that goes on in the Bible. Or thinking homosexuality is a sin even though Jesus never said anything about it, but just completely ignoring other parts of the old testament.

Hell, the Bible contradicts itself on the order in which God created the plants and animals.

You...picked very poor examples of problems with the Bible.  The commandment against killing is better translated as a commandment against murder, which is by definition extralegal killing.  There's extensive laws regarding legal killing, and the commandment rules out killing outside of those rules.

As for the homosexuality thing, "what Jesus said" is hardly the basis of Christian doctrine on most points.  In this case, St. Paul's epistles are pretty clear in terms of upholding and even strengthening the OT rules.

EDIT: A better example of a bona fide Biblical contradiction is the confusion over whether Noah took 2 of each animal or 7 of each animal on the ark (though that has a reasonable-enough explanation offered that Noah took 7 of every clean animal and 2 of all the unclean animals).

[The Mikado]

Joseph Smith NEVER taught that; he in fact ordained several black priesthood holders, and in his presidential campaign expressed the idea that slavery should be phased out. So clearly, the black priesthood ban was never real doctrine.

When you say "phased out" do you mean like the Latin American solution of having the children of slaves be free from birth but maintaining slavery for current slaves, or do you mean something else?  Curious because I never knew that about Smith.

[The Mikado]

Mormonism was created a couple centuries ago by an ego-maniac with a ridiculous story.  We had made quite a but of progress as a species. 

Ah, the triumphalism of positivism.  "Progress" indeed!  Unlike those ignorant Bronze Age savages, we know how to kill each other in more economical and efficient ways than ever!  While those morons died of smallpox, we invented the tools to first eradicate it, then used those tools to weaponize it and singlehandedly restore the fear of smallpox to the world!