T. A. Gardner
Serial Thread Killer
It is not about "disclaiming" the possibility, it is about the necessity. If an "intelligence" is, in fact, directing the evolution, we would see some kind of evidence.
Consider the junkyard tornado, also known as Hoyle's fallacy.
If 747 is assembled, you can be certain intelligence was behind it.
Why? If the intelligence were sufficiently, well, intelligent, couldn't it make it look like it was not intelligently designed? You are using the McNamara fallacy. That is, you are saying if it can't be quantified or identified as intelligent while discounting any other explanations then it isn't intelligent design.
Intelligent design doesn't require Hoyle's fallacy either. Why? Because an intelligent designer over millennia might slowly change things bit by bit watching the outcome before moving to the next change. It doesn't have to occur all at once for intelligent design to be present.