This "theory" supposes that because life is so complex in its physical manifestations, there must have been some "designer being" (God) to make it all happen.
I have a question: How complex is complex enough to have required a designer?
I think proponents of IS have it backwards. Anyone who tries to design something for functioning endeavors to make the design as simple as possible. Complexity increases to possibility of error and/or breakdown. Research of DNA has revealed an excess of complexity, in other words, the instruction sets for life forms contain irrelevant and obsolete segments.
What might actually have revealed intelligent design would be the simplest possible instruction set required to produce a given life form. This happens to not be the case.
The "theory" of intelligent design reveals an inherent flaw of its own. It's too simple to account for much of what actually exists. It is not an intelligent theory.