The idea is for his character to get worse and worse until you can no longer feel any empathy for him. This scene and the very last shot of the last episode are meant to convey that.
Its also noteworthy that Walt has now killed about seven people. In the first season he used to bitch and rant about no bloodshed. In the last Ep. he's now walking stone-cold brutal. His victims are hardly worth a second look, as evidenced by the pop-and-drop of the guard in the lab, left in a heap and he steps right over the corpse.
By mid-season next year, I fully expect him to be Jason Voorhees. I imagine it'll have to culminate with Walt killing Jesse, and probably Hank. And probably Skylar (she's got a big moral stick up her ass). And probably Saul. And probably whoever the fuck else needs killin'.
Even Jesse is coming around to this.. "You brought a bomb
into a hospital?" The guy is just completely monstrous.
Hence the title of the show.