My thought is that White's sickness (it's cancer, plus) does in fact "mirror America," but in a much more general way than Sirota says.
As Sirota notes, Walter White starts out as a well-intentioned person, trying to provide for and protect his family, and goes from there deeply into criminality and violence. By season four, I have found that my initial sympathy for White has much diminished.
If America were to look in the mirror, I think the country might well reach the same judgment about its own national conduct.
Initial good intentions don't excuse, and I can't believe, from my perspective in season four, that the ending is going to be any species of redemption. When you find that you are "breaking bad," you had better start that other kind of "braking." And the sooner the better. Sometimes you get so far gone you can't get back. It's too late then.