A point I try to make sometimes but possibly not as clearly as I should: Creationism is not just patently stupid on an intellectual level; it is also abhorrent on a moral and emotional level. Let me explain why I feel this way:

Both Creationists and evolutionists (I use the term begrudgingly) acknowledge…

• Our DNA determines what we are as humans more than any other factor— If you replace the DNA in a human zygote with that from a different species (and manage to get a viable embryo) the resultant organism will not be human.
• A person’s DNA is inherited directly from their mother and father, 23 chromosomes from the mother and 23 from the father.
• DNA experiences mutations, randomly as well as through environmental factors.

From this point on, opinions differ…

• Evolutionists know that mutations are not always bad, and that without them we would never have progressed beyond the primordial ooze. Through accidental duplication of DNA and horizontal gene transfer new material can be added, and in turn this can lead to new forms and new functionality.
• Creationists assert that mutations can never add new information, and will always lead to degradation of the organism.

Therefore…

• Evolutionists believe that humans, like any other species, are capable of adapting over time to fit their environment, that we are effectively always "improving" ourselves, by the simple fact that organisms better suited to their environment have a higher chance of survival and are more likely to produce viable offspring.
• Creationists believe that Man was created in his ideal form, that all of our genetic material originated within Adam and Eve, and that it has been deteriorating and degrading ever since. They don’t accept that random change could improve on God’s handiwork. From this it follows that every generation must be more corrupt, more degenerate than the last— in essence there is only de-volution.

I bring this up not as evidence in support of the fact of evolution, but as a rebuttal to the common appeal to emotion offered by Creationists— that an evolutionary view is somehow ugly and without hope. I counter with the question: is it really more hopeless than the idea that we are doomed to be eternally inferior to our forebears, who committed some kind of symbolic sin against a selfish and wrathful God? This view of humanity as a species doomed to rot fits quite well with Christian doctrine, in that men of the Old Testament routinely lived many hundreds of years, remaining strong and producing children for most of their extraordinarily long lives, and were closer to God than anyone today.

Creationists often try to blame evolutionary theory for the unimaginable evil of the Nazi Holocaust, even though the engine of evolution thrives on diversity, and recogizes purity as at best a meaningless concept, and at worst a dead end. On the other hand, if you believe that you are descended from some mythically superior race, it makes a lot more sense to strive for some kind of fantastical racial purity.

Creationism taken to its logical conclusion offers an extraordinarily pessimistic and self-hating view of humanity, and it deserves to be scorned. The evolutionary view is by contrast rather optimistic— how incredible that we could come so far! Life appears to have limitless potential, filling every available niche and boggling the imagination with its variety and tenacity. And it belongs to no one. It is beholden to no one. According to evolution, the future is not written, and we as a species are truly free to find our own purpose, and be the authors of our own destiny.