Let's say your preschooler asks you, "Where do babies come from? How did I get here?"
There are a number of ways you might answer, but if you know anything about young kids, you are not going to give your child all the details of human reproductive physiology and adult sexual behavior. Your child simply hasn't developed enough intellectually and emotionally to take in, much less process that kind of information. You're going to say something that meets your child's intellectual, emotional and spiritual needs right now. The details can wait until the child is more mature.
Now let's flash back some 2,800 years. You are God, and the Hebrew tribes are beginning to wonder how the world and humankind came into existence. One thing you are not going to say to them is, "First you need to learn Quantum Mechanics...." It would make absolutely no intellectual sense to them, and it would be too sterile emotionally and spiritually. You're going to tell them something that captures the essential truths of their relationship with you in a way that has meaning for them. Maybe that you made the Universe and everything in it. That you didn't make it all at once, but in stages. And lastly, you made people. And you made them special, so that you could even have this conversation. The details can wait until their cultures mature enough that they can discover Quantum Mechanics on their own.
In other words, the Creation story in Genesis is true. It's truth is similar to the truth a conscientious and loving parent might tell a five year old child about sex.
We could insist that a five-year-old's understanding of human reproduction be taught in high school sex education courses. But high schoolers, knowing more than that already, would see us as idiots, which would undermine our authority to teach them anything, period. Insisting that an iron-age understanding of biology be taught in 21st century high schools is of the same order of idiocy, and - for most kids - undermines our teaching authority in the same way.
So while Creation is true (in this Christian physicist's opinion), Creationism is false. Creationism insists that the iron-age understanding of cosmogeny and biology is factual, to the detriment of its true meaning for all of us. The Creationists and their spawn, Intelligent Design proponents, are not disingenuous, they're just wrong. They're telling an honest lie.