Introduction
Not all creationists are creation scientists. A creationist is, at his or her core, someone who believes that a Deity individually created the animal and plant species we see on the world today. There are Apache creationists, African tribal creationists, Christian creationists, Muslim creationists, etc. and these groups have wildly incompatible beliefs.
Likewise, not all scientists are atheists. I knew many churchgoing biology professors at my college who had no trouble reconciling their religious beliefs with the fact of evolution; one scientist told me, "Science explains the how, religion explains the why." These men and women understand the power of a metaphor. Evolution contradicts nothing in the Bible on a metaphorical level (of course fundamentalist Christians insist on reading the text literally, which creates all manner of sticky continuity issues).
Creation science is a pseudoscience aimed at "proving" the religious belief that their God literally created all life on the planet in a more or less immutable form. For the purposes of this writeup, the creation science I'm referring to is the variety propagated by American Christian creationist groups, particularly the intelligent design group. They have been extremely clever and efficent at making their philosophy seem scientific to the voting public, and as a result they've been able to sway many a school board in this country to include their beliefs in school science curricula. Ultimately, their aim is to preserve the literal interpretation of the Book of Genesis.
Some extreme Christian creationists reject science entirely; among them you will find people who still believe that the Earth is flat and folks who believe that the Sun (and the rest of the Universe) revolves around the Earth. You will find among them people who would rather let a child die of an infection than take her to the doctor for antibiotics.
While mainstream Americans can (and generally do) dismiss folks with such extreme and easily-disproven notions, the intelligent design group is much more sophisticated and their arguments much more polished and convincing. Their public speakers all have advanced science degrees, and they are excellent orators. In the olden days, you'd see creationists exclaiming that "The Devil put dinosaur bones in the Earth to confuse you!" Today, they get into some fairly high-level debates over finer points of molecular biology; one virtually has to have a biology degree to understand how they're twisting the evidence.
But they're still selling the same fundamentalist ideology under a scientific disguise.
Ideological Issues
I knew a few people in high school and college who subscribed to creation science; they told me they believed evolution is fake. I talked with them and what it came down to was that they didn't want to believe that they're descended from critters that crawled out of the muck a billion years ago (how this is worse than being descended from a gent who was made from a handful of dirt, I'm not sure.)
Creationists don't want to think that, biologically speaking, the monkeys are our country cousins. They want to be special. They insist that we are God's chosen, that humans are not animals.
This may not seem like a big ideological problem, but it troubles me. Belief that you are one of God's chosen is a mental license to do reckless things, such as exhausting your natural resources and hunting other species to extinction (in the 1700s and 1800s, people refused to believe that hunting could drive animals to extinction; they were sure God wouldn't allow one of His creatures to be gone forever. And so went Steller's Sea Cow and many, many others).
If you think that you are not an animal, you will also probably believe that you are "above" the problems the rest of the world has and that you are somehow apart from the planet's ecology and environment. And if you think that you're God's chosen, won't you also think that He'll eventually bail you out if things go wrong? Is expecting to be bailed out of your problems conducive to really trying to solve them on your own?
And if you believe in Armageddon, believe that God will eventually destroy the Earth and send all his chosen ones to Heaven, can you really be committed to trying to keep society and the planet fit for future generations?
I think that this kind of fundamentalist Christian belief has as much effect on the public's behavior as social construction supposedly has on science. And I see public acceptance of evolution as reality as key to our society's truly coming to grips with our environmental and ecological problems and really making a commitment to do something constructive about them.
All the biologists I've ever known have related the same experience in their youth when they first learned of evolution: "Oh my God, everything makes so much sense now! The interconnectedness of all living things, gosh, the world is such a cool place."
Nothing in the field of biology would make any sense at all without the underlying principle of evolution. Nothing.
We don't necessarily know how evolution works, but it's as much a fact as water being wet or the sky being blue. It's just not as obvious because of the huge expanses of time involved. Humans aren't built to truly comprehend a thousand years, much less a billion. And too many people assume that, because they can't wrap their minds around an idea, the idea can't be true.
Scientific Issues
Creation science is not science because it is not falsifiable.
And regrettably, few laypersons truly understand what falsifiability means. Scientists have to try really, really hard to disprove their own hypotheses before any other scientists will take their research seriously. Real science involves actively seeking out results contrary to what you're trying to show.
In basic terms, if you've hypothesized that your pitcher has no leaks, you fill it up with water and see if anything leaks out. And then you X-ray it, then fill it with alcohol, and so on until you can prove that your pitcher is solid.
Creationists never try to disprove their beliefs; they only use data that supports their cause. Their coveted, cracked pitchers are safe on the shelf, wrapped in newspaper articles. They insist that their crockery is solid, and say they don't need to bring it out to prove it. Occasionally, they get a "scientist" (i.e. somebody with a Master's degree in science education or physical science) to take down a pitcher, carefully fill it with sand, and hold it up, proudly declaring, "Look folks, no holes!"
Switching metaphors, let's consider this hypothetical passage in the Bible: "And on the Second Day, God created the Heavens, and He painted the sky blue, for God favoreth that color." (Hey, it could have been written that way.)
Anyhow, other than the obvious results of this passage (picture a blue Bible and blue-coated ministers) imagine the ramification of scientists discovering that the sky appears blue due to Rayleigh scattering in ozone and other atmospheric gases.
"The ozone layer is a lie!" The strict Biblical interpretationists would cry. "God painted it blue! It's blue because of paint!"
Scientists might reply, "No, really, there's ozone up there. It's true; it protects us from solar radiation. The idea that it's paint is silly. But perhaps the ozone layer and other gases are God's way of 'painting' the sky blue?"
"No!" The paintists cry. "The Bible says it's paint, so it's paint! Ozone is a lie."
"Uh, by the way," other scientists interject, "We seem to be having a problem with the ozone layer ... it's breaking down. We need to do something to stop this ozone loss, or we'll be exposed to too much radiation."
"Ha!" say the paintists. "The sky is still blue -- how can this so-called ozone layer be breaking down then? The holes are in your 'theory,' not in the sky. There's no danger from radiation. God will protect the faithful."
Meanwhile, one sees "objective" articles in magazines and newspapers very mildly (and inaccurately) suggesting that "most scientists don't believe the sky is painted blue. Most believe the blue color results from a very thin layer of a chemical called ozone."
And so it might go. The argument rages unproductively as melanomas blossom and crops wither.
It really is that cut-and-dried, scientifically speaking. After all, the whole ozone depletion situation is still up in the air (excuse the pun), but we know ozone is real (just ask iceowl about the raging sunburn you get down in the Antarctic). Evolution is just as real, though (as with many other complex scientific issues) our understanding of it is far from complete.
I've heard people asking if there is any scientific "alternative" to evolution. That's a bit like asking if there's an "alternative" to gravity or aging. Evolution is a documented natural process and scientists are trying to sort out how it works. Dissent over evolution in the scientific community deals with the particulars of evolution (for instance, is it gradual, or do species change in sudden leaps?) rather than over whether or not evolution is real. Creationists such as the intelligent design proponents warp the nature of the scientific dissent in order to make their pseudoscience seem reasonable to the public.
Cold, Hard FAQs
nocte took me to task for not including any "hard facts" about evolutionary issues in this writeup. Fair enough, but entire 300-page textbooks are regularly written on the subject, and anything shorter would be in many senses reinventing the wheel here at e2. So, I point those of you seeking further factual information to: