We use ID theory in every day life. Say I come across a book on the sidewalk. Should I conclude that the book was written by an intelligent agency (a human being) or that it spontaneously assembled itself by some as yet unknown natural process? Which theory regarding the book's origins is a better "scientific theory"?
Similarly, we see examples of irreducible complexity in the natural world. One well known example is the bacterial flagella.
From Is Intelligent Design Testable? by William Dembski
FALSIFIABILITY: Is intelligent design falsifiable? Is Darwinism falsifiable? Yes to the first question, no to the second. Intelligent design is eminently falsifiable. Specified complexity in general and irreducible complexity in biology are within the theory of intelligent design the key markers of intelligent agency. If it could be shown that biological systems like the bacterial flagellum that are wonderfully complex, elegant, and integrated could have been formed by a gradual Darwinian process (which by definition is non-telic), then intelligent design would be falsified on the general grounds that one doesn't invoke intelligent causes when purely natural causes will do. In that case Occam's razor finishes off intelligent design quite nicely.