That phrase has an almost magical ability to intimidate theists.
Even though the argument has been convincingly refuted time and again, it lives on in the popular literature.
Ironically, when critics make this accusation, they are usually committing a “gaps” fallacy themselves.
The theory of intelligent design begins with observations of how intelligent agents act when designing things. By observing human intelligent agents, there is actually quite a bit we can learn know and understand about the actions of intelligent designers.