[why would God give a whale lungs, placental reproduction, live birth where the mother must lift the baby up to breath, and mammary glands instead of the design of a fish? God even gave the whale the underlying skeleton homologous to other mammals, instead of one of a fish.]

why not? There are trillions of different designs, features and abilities in nature. The simple answer is diversity. God, it seems to me, loves demonstrating Himself by making unique and diverse works of art. And the funny thing is, keeping with mammals, is that all mammals share pretty much the same set of genes, no matter what they look like. It's almost like God is playing with scientists, like humans can play with cats with a piece of yarn. The idea that a mammal one day decided to start playing in the ocean and then evolve new and different traits so that he could one day swim in the depths strikes me as lunacy.