The Key Metric
One of the most important ideas, or key metrics, in engineering is efficiency. This idea can be subdivided into two more detailed ideas called efficiency of form and efficiency of function. What this means is that first a design must be efficient in that it utilizes a minimal amount of materials and labor to maximize its performance. For a building, this means it should be designed to utilize the minimum amount of materials such as timber or steel girders and the minimum amount of workers to construct the building. The next idea in place is efficiency of functionality which means that the structure should serve its designed purpose and require only a bare minimum of upkeep and maintenance. If it costs more to maintain a building, such as a hotel, than the building can generate revenue to sustain itself, then we must say it is inefficient and is a poor design.
This is the guidebook for intelligent design. It is the only blueprint we have by which to gauge what intelligent design is. The only examples we have of things that we know are intelligently designed are the things which we humans have designed ourselves. Buildings, watches, cars, clothing, and everything else we humans have designed have come from intelligent minds. We see these items fail to be efficient and we see them refined and improved upon so to become ever more efficient. The fact is, we must constantly improve our designs the more we learn in a constant quest for greater efficiency. The natural world around us must do this also, because of the restrictions of physics the natural world must work towards efficiency, always battling with forces such as friction and gravity which can impede efficiency.
Examining the Philosophical Implications
So, how this applies as an argument against intelligent design comes in the form of a philosophical application of comparison. You see, when we compare the observable universe with the known intelligent designs of humans in relation to the key metric of efficiency, we see a great disparity between the two. The observable universe does not show us a model of designed efficiency. Instead, what we see is a universe striving against natural forces to achieve some semblance of efficiency. The very fact that the universe must fine tune to strive towards efficiency is a serious problem for intelligent design proponents.
Here's an analogy:
If I build an aquarium the size of several football fields and then put only one goldfish in this massive space, we can most definitely claim that this habitat was designed - but claiming that it is intelligently designed would be absolutely fallacious.
This is exactly the proposal that intelligent design proponents want to put forward. They want to say that because the universe had a beginning it must have a creator, and because so many things around us are so complex, this creator must be intelligent. But there is nothing intelligent about creating an entire universe where life is more rare than anything else we've ever discovered. That is a complete waste of resources and totally inefficient and to claim that this is the work of an intelligent being is to claim that silly little humans like myself have a greater understanding of efficiency and design than a being who can create universes - and quite frankly this is an insult to the very idea of intelligence itself.
Now, at this point I have to offer a concession. You see, I have no argument against something setting the universe in motion. Furthermore, it is not impossible or implausible that whatever set the universe in motion was an intelligent being. But this only offers that it is possible that some scientific minded being set an experiment in motion and that life is a byproduct of that experiment. That's it. And in the end, this only poses more questions than it answers - like where did that being come from?
Understanding the Argument
I want to make it clear that this is a philosophical argument. This isn't some supposedly scientific proof of the non-existence of God. In the end, all any of us can offer are these philosophical arguments because mankind has yet to find any scientific measure of god. There are no definitive answers, and any man who offers you such is either a liar or a fool - quite often both. It is up to each of us to judge the merits of these arguments for ourselves and decide what sounds acceptable for us. For me, the idea of an intelligence behind the universe doesn't fit with the observable facts and I wonder how others don't see this. Regardless, I can no more claim to be absolutely sure in my position than anyone else.
There is no need for philosophy in order to show the falsehoods of the major religions. Each of them has an abundance of flaws in both factual accuracy and philosophy. They undo themselves if one truly studies them in contrast to reality. But the deistic idea of God is still powerful, and it is born of notions such as the teleological or cosmological arguments that posit the idea that we must have a creator of our universe. I see no sufficient evidence of this at all, and I most certainly see no intelligence guiding any of it.
In its simplest terms my argument is this; Under the idea of Intelligent design, every planet that doesn't harbor life is an absolute waste. Every star that doesn't form a solar system around it is a waste. In short, your god built an aquarium for just us little goldfish and that isn't intelligent - it's asinine. But, if the universe is a naturally occurring and naturally evolving thing, as science clearly shows it is, then all of this makes sense. The scarcity of life in this universe simply negates the notion of intelligent design.
I want to share with you here a lecture in which Neil deGrasse Tyson makes a similar case, and maybe you'll find his words a bit more entertaining than my own.
For a more in depth look at this topic check out Casper's book "The Engineer's Argument"