One of the many, many things I like about Breaking Bad is that it sets up that comfortable, familiar trope that evil can be justified by the "fundamental nobility" of protecting the people you love and then spends the rest of the series systematically kicking the shit out of it. Walter White is (aha) a cancer, spreading to poison everything around him both literally and figuratively. It tells us that just looking out for you and yours at the expense of society at large doesn't make you noble, it makes you a monster.

The show presents Walter as A Good Man Driven To Desperate Ends but then almost immediately starts undermining that impression. It's not cancer that starts him cooking meth, it's pride. In the second (third?) episode of the series he's offered a lucrative job that will ensure he gets the best possible treatment for his condition, and he turns it down because it's not making sure that his family are provided for that matters to Walter, it's that HE provides for his family. Everything that follows, all the people who get directly, indirectly or casually fucked by the ripple-effects of the meth business aren't victims of Walter's love for his wife and son, they're victims of his hypocricy and towering ego.

That desire for control and its flip side, the desperate need to be appreciated for what he's done, not only puts him on the path to becoming Heisenberg but is also at the core of pretty much every fucked-up situation in the series. Walter thinks he's the smartest guy in every room (and he's frequently right) and thinks he can see all the angles (and he's frequently wrong). Over and over he's sure that everything will be safe, smooth sailing if he can just achieve... something. Killing Tuco, selling meth as well as making it, getting into partnership with Gus, killing Gale, killing Gus, robbing the train - every time Heisenberg is absolutely certain (aha) it's the last thing he needs to do to make things work and every time there are unintended concequences that prove him spectacularly wrong. Not only does he fail to learn from these mistakes, he actually gets worse so that by the end of Season 4 his ego has almost completely consumed him. He's wearing his Heisenberg outfit even at home because he doesn't want to be Walter White the father, husband and provider. He wants to be Heisenberg, the shadowy mastermind who's respected and feared. He's the one who knocks. He's in the empire business. Say his name. Say it.

In the wake of shooting Mike, Walter finally has a moment of clarity and catches a glimpse of who he's become. Possibly in combination with a recurrance of his cancer it drives him to try and climb out of the hole he's dug for himself but once again he's betrayed by his own hubris. Walter has pulled the wool over Hank's eyes so often he's stopped seeing his brother-in-law as a threat and so leaves incriminating evidence lying around in plain sight. And so finally it's Walter, rather than everyone around him, who's about to reap what he's sowed for the last four seasons.

tl,dr - Walter White: fuck that guy.