I just watched Flock of Dodos: The Evolution-Intelligent Design Circus. It's probably the first documentary on the subject that I've seen which manages to give nearly equal time to those who promote evolutionary theory and those who want intelligent design to be taught along side it or in place of it in schools.
Without any help from the filmmakers, those in favour of intelligent design have managed to make themselves look like idiots. It was pointed out in the film that they've got an idea that is not necessarily a bad idea, but they've not bothered to go any further with it, whereas scientists take their ideas to the hypothesis stages and through to the stages where it is either nearly proved or disproved, and this requires repeated study to ensure results are consistent. Intelligent design hasn't gotten to the hypothesis testing stages yet.
It is generally accepted, from what I understand, that the theory of the big bang mathematically makes sense up to a very tiny fraction of a second after the event occurred. It is unknown what happened before that or what the catalyst was. The rest of it makes sense (if you can understand the math involved). Evolution is even more tangible for those of us who aren't trained scientists. You can hold a fossil in your hands and see where it changes to the next fossil formation several thousand years later, and it is often quite clear how the two are related.
Yes, there are some unknowns. Yes, it is okay to insert your faith into those gaps that exist. No, it is not okay to teach kids that is why there are gaps. A hundred years ago we had more gaps that we've been able to fill. Five hundred years ago we had even more. We've managed to fill them through tested hypotheses, data collection, and so on. Tomorrow we may have found the missing link in the evolutionary development of mankind. What will the intelligent design people do then? They'll have to push their deity out of the gap that no longer exists.
If we teach kids intelligent design along with evolution as a separate theory, it confuses and clouds what we already know. It may even cause some kids to decide there's no point in trying to make further discovery, because the gaps are filled by intangible faith. This is not helpful in understanding how the universe works nor is it helpful in furthering progress or scientific discovery.
Those who support intelligent design refuse to admit that it is repackaged creationism, but that's exactly what it is. The only difference is that now they accept what we know about the evolutionary process as correct, but those things we can't explain yet must be taken on faith and to move on. That makes no sense. The history of the universe, how things work, and all the things that make scientists study what they do doesn't tend toward faith.
The gaps are missing puzzle pieces. All that remains is finding them, but we can't do that so long as we have people wasting valuable time and energy in trying to make rational people accept a so-called theory that isn't rational in the least aside from the major portions that were proven via the very thing they're trying to hamper - rational science!