They do. It's required.
A possible re-construction of history by comparative morphology of the genome or the fossil record requires inferential leaps of faith that may be reasonable, but they are not empirical. Possibilities and probabilities of intelligent design also require inferential leaps of faith when organized matter that performs specific functions is recognized. Neither common descent nor intelligent design are, in the strict sense, empirical science. They only make use of empirical science, from which they make reasonable conjecture.