The plan was always for this to be a man's slow descent, nothing was sped up. Walt did amoral shit in the first three seasons too, let's not kid ourselves. It was obvious he'd have to essentially ramp up towards the end, given his cancer and the threats to his family.
On a side note I find it interesting that people identify and root for Walter White and Tony Soprano, yet one of the biggest reasons The Wire never was a big show while it aired was because it challenged viewers to identify with black drug dealers. There's just as much humanity and personality in a lot of the characters, they're just as grey...yet at the time I remember a lot of people not wanting to "root" for "drug dealers." Just an interesting aside, to me at least. Obviously now everyone loves The Wire, but it wasn't always like this.
