Most individuals who were living at the time of Captain Ahab and who were religious would have believed that blasphemy was a mortal sin, punishable by condemnation to the everlasting fire of hell. This would be a tremendous punishment to be avoided at all costs.
Captain Ahab, however, did not care about the possible consequences of blasphemy, or any other sin. He refused to suffer insults, challenges to his authority, or arguments against the plausibility of his vendetta against the great white whale. He was willing to risk the fire of hell or the fire of the sun if he was crossed.
Ahab was driven by his obsession with the revenge he wanted to exact from Moby Dick. He demanded of his crew what he demanded of himself - absolute commitment to the achieving of the goal. He had no patience for distractions from the hunt and the fight. He was completely dedicated to the purpose he set for himself.