I think he definitely has. I've always loved the contrast between Walt and Jesse's characters. Jesse is the one who society would typically consider to be a bad person. He deals drugs and is viewed in some ways as a leech of society. Jesse, however, shows excellent moral character. He sees the importance of a life and hopes to avoid any harm coming to other people. Walt is the one who society typically views positively. He is a high school teacher and father of two. Walt, however, seems to kill needlessly and without the slightest hesitation. There were two moments that truly proved that Walt had lost all morality. SPOILER: The first was when Walt shot Mike out of pure anger and then proceeded to hide it. It was an unnecessary, pointless death that could have been avoided. The second was when Walt not only revealed Jesse's hiding place to the neo-nazi crew after Hank's death, but then proceeded to rub Jane's death into Jesse's face. That was pure cruelty. Walt may not have started as a bad person, but in the end there was virtually no good left in him.