The recent debate about Intelligent Design seems to revolve around the delusion that the theory is religiously motivated. Personally I was born into communism, where I wasn't exposed to creationist doctrines, yet reason told me that the common descent of life's complexity from a simple beginning makes absolutely no scientific sense.
The Principle of Causality -- having no relationship to creationism, fundamentalism, or any kind of ism -- stipulates that no cause can produce an effect superior to itself, or give more than what it has. If a cause could produce anything greater than itself, the extra part of the effect would be without a cause, and that is contrary to reason -- and, by extension, to rational science.
So the Principle of Causality tells us that when we try to derive the richness of life from a simple beginning, as Darwin did, we are deluding ourselves. We try to get from a simple cause what it clearly does not have, namely greater complexity. If a simple beginning could in fact cause greater complexity than itself, then it would invalidate the cause-and-effect relationship. As science is, above all else, about cause-and-effect relationship, the true test of a theory or explanation in science is the central question: Is the proposed cause of a phenomenon sufficient to bring about the effect attributed to it?
Knowing that complexity's evolution from any kind of inferior cause is irrational, we have no choice but to propose that the initial cause of the universe can be no lesser in qualities than the qualities we find in the universe. Thus this logical inference from a highly complex effect to a cause no lesser in complexity than the effect itself points in the direction of an agent that we may call the parent seed, common ancestor, or cosmic genotype of the phenotype universe.
Because logically the existing most advanced form of life constitutes the cosmic system's input and output -- just as an acorn constitutes the mighty oak's input and output --, and because we have no knowledge of a more advanced life form than human life, the necessary inference is that human life or intelligence generated the universe for the production of human life in its own image, just as a seed generates a tree for the purpose of self-reproduction.
Thus, whereas the theory of evolution posits common descent from a simple beginning, the scientific theory of creation posits common descent from the most advanced form of life that exists. As we have no confirmable evidence that a life form superior to human life exists, we are constrained to propose that human life constitutes the seed of the universe, pending the discovery of a superior non-human form of life.
Of course it is not mandatory to take it for granted that human life constitutes the seed of the universe. This theory of creation is testable and can be falsified. After all the proposed sole actor, namely human life, most definitely exists, and is available for observations and experiments.
To conclude, if we posit common descent from the highest form of life that exists, we have a rational theory which is consistent with the data we have.
In any case the good news is that when circumstances force Americans to think seriously, the majority reaches the right conclusion. Namely, a November 2004 Gallup poll found, that only 13% of respondents said they believed that Intelligence had no part in the evolution or creation of human beings.