If I were an all powerful being who wanted to create something as big and beautiful as the ENTIRE UNIVERSE... I would NEVER do it all by hand. I'd be too smart for that. First, I'd create the Laws of Physics, chemistry, etc. Then I would design a mechanism by which life of all forms can flourish.... IE... Evolution.
To me, Evolution is proof of creationism. It is proof that there is an Omniscient, Omnipotent being out there.
Most people who don't believe in evolution say "it's just a theory, it hasn't been proven" Which is a blatant misunderstanding of the word "theory". In scientific terms, a theory is something that has been proven, but not quantified (As opposed to a Law which is always true in every instance and can be calculated). It happens folks. No amount of whining and moaning can un-prove or undo evolution. So instead of believing that it is some affront to God, why not realize that Evolution is actually God's work?
We've seen evolution in our lifetimes. On microbial scale, we see things like algae being coaxed into evolving into fuel producing species. As humans, we've had a hand in the evolution of Dogs. We chose the ones that are loyal and that look nice, and the rest were routinely killed off. Even an astute person can see how traits are passed down from human parent to human child. We see hundreds or thousands of versions of the same plants and animals in different regions of the world.
So lets look at this differently.
Evolution does not disprove creationism, it is the mechanism. Science is how were discover God's universe. It is not the unholy tool by which we unravel God. It is God's tool by which we discover HIM!
In rebuttal to the title of the thread, not everyone does think that evolution contradicts creationism. That said, I know that evolution is a falsity. I believe the Inspired Version of the Bible. It is a version that was given by the Spirit of God to Joseph Smith. Mostly there are changes to the Genesis account, and a few changes in the gospels. One of the changes is in the story of God's creation and the reason that there are two stories that are told of it (or that there is a reason at all, as it is not explained in the KJV). It says that there was a spiritual creation before there was a physical one. It says that the soul is the union of the spirit with the body. It says that every one of God's creation was created in spiritual form, yet there was not a man to till the ground.
From chapter two of the book of Genesis:
6 And I, the Lord God, had created all the children of men, and not yet a man to till the ground, for in heaven created I them, and there was not yet flesh upon the earth, neither in the water, neither in the air;
7 But I, the Lord God, spake, and there went up a mist from the earth, and watered the whole face of the ground.
8 And I, the Lord God, formed man from the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul; the first flesh upon the earth, the first man also;
Notice, Adam was the first flesh upon the earth. This leaves no room for equivocation. There is not any wiggle room. Jesus speaks of Adam as a real and living being as well. In order to dismiss Adam as an amalgamation of man in general or an illustration I must also dismiss Jesus words as those of a mistaken individual, which he cannot be and still have lived a perfect life. So, take your pick. Either one points toward a real Adam created in time and space.