On what basis does ishmael justify hypothetically deifying the sperm whale

Did you mean "defining" the whale?

no its deifying

Once again Melville and Ishmael exalt the Sperm Whale for its ability to resist definition; in its "pyramidical" silence, the whale does nothing to offer itself for interpretation or to prove its genius, but rather stands as a monument to its own greatness. Melville continues to describe the whale as a thing that is unnaturally made, with the comparisons to the pyramids and other constructed objects.