To simply put, ID is just lazy thinking. Just imagine the following questions and answers.
Q: How does the lipid bi-layer of a cell keep itself together while allowing certain molecules to pass into and out of the cell?
A: An intelligent designer designed it that way.
Q: How do birds know which way to fly when they do their yearly migration?
A: An intelligent designer designed it that way.
Q: Why is the pythagorean theorem true for every right triangle?
A: An intelligent designer designed it that way.
Q: Why do many languages in certain regions are so much alike? For example, Italian and Spanish.
A: An intelligent designer designed it that way.
Q: Why do we see a rainbow everytime there's sunlight and rain?
A: An intelligent designer designed it that way.
The answer is just a simple modified version of the typical "goddunit" answer many adults give to their children everytime they ask curious questions. I grew up being force fed the "goddunit" answer. I entered high school and college believing the world operated on god's magic and that there was little more explanation for what goes on with planetary motion or biology than "goddunit".
What ID proposes is institutionalizing lazy thinking. By giving the answer "an intelligent designer designed it that way" everytime a phenomenon is encountered that at the moment cannot be understood, progress is permanently suspended.
I once attended a lecture by a very famous philosopher of science (can't remember his name). His lecture was on how ID attacks science and intellectual progress. One of the things he pointed out was this: Let's say that an intelligent designer designed the biological processes we see today. Then what? The so-called discipline of Intelligent Design leads to nowhere. Neither the scientific community nor the intelligent design advocates could name a single foreseeable progress made to science or humanity with Intelligent Design. Its very nature is to impede progress by savoring ignorance.