It's not that many deny evolution; they deny it is proved 100%. There are still holes that can not be explained in it.
Also, even if, perhaps when, evolution is proved biologically, science can never explain the soul.
Personally, I do not think that evolution negates creation or vice-versa.
Because although the theory of evolution is heavily supported by evidence, it is still just a theory and not a fact. Don't get me wrong, I'm agnostic, but since Evolution hasn't been completely proved, creationists are still able to cling to their beliefs. In the case of the heliocentric solar system, there is now undeniable proof that the we revolve around the sun. If there was some doubt in the system, then creationists would completely reject it. I'm not really sure, but I think there are still people who reject the idea of a heliocentric solar system.
Mate, back in the days creationists didn't accept the theory that the Earth was rounded or not in the centre of the universe despite overwhelming evidence. It's not just evolution they singled out.
Over time, people will begin to accept evolution too. But such progress only occurs very slowly. And then they'll start attacking another scientific fact.
I think it's because there is no logical process behind their thinking. They just seem to pick bits here and there that fit into their warped view of the world and then just make up the rest to fit.
Fear. Being told all of your life you are a Special Creation only to discover you're just an upright mammal conflicts with their egos.
Greg, read the question again, please. He specifically asks about creationists- hardly a generalization. There are Christian and Muslim creationists. One of the most dangerous Islamic creationists is the Turkish charlatan Adnan Oktar, who goes by the nome de plume Harun Yahya and has great appeal in the Islamic world. He's currently in a Turkish prison but if you check his website at http://www.harunyahya.com you'll see his large gang of support is still at it.
Creationism does not equal Christianity. My own scientist father was an evolutionist.