Why does Starbuck accuse Captain Ahab of blasphemy?

My guess? Because Moby Dick is a beast that acts only on instinct. Ahab treats it as if it were a man who had wronged him. Man was made in the image of God; Ahab’s acrimonious attitude is tantamount to saying that the whale, too, was made in the image of God.
God did not make whales in His image, and saying that He did is insulting.

I dunno, I never actually read Moby Dick.

I think Starbuck accuses Ahab of blasphemy because of his obsession for finding Moby Dick. I’m not sure if this is strictly a Quaker definition at all, but the intensity/fervor/passion whatever that Ahab displays should be towards God, not a whale or anything else. I’m not sure how faithful the movie is the to the novel, but the captain has a quote somewhere where he says something about how he’d fight the sun, even, if it disrespected him.

I think @Nullo‘s got an interesting take on it too.

Moby-Dick, the Great White, symbolizes God. (If you read about Herman Melville’s life, it is easier to understand what Starbuck meant and why Melville wrote this into the novel.) In the novel, Ahab baptizes the harpoon he plans to revenge his “God” with by anointing the harpoon with the blood of his pagan harpooners. The blasphemy comes in Ahab thinking himself better than God; just like Lucifer. Ahab thinks he’s omnipotent and the pious Starbuck realizes this about Ahab. Starbuck also has a healthy respect for not only God, but nature and the power of Moby-Dick.

The first words of the novel, “Call me Ishmael,” set the scene for the religious symbolism. The novel ends with the opening chapter of the book of Job from the Bible.

You should read it sometime @Nullo.