When Sam makes the comment about how he thought the angels would be different because they are suppose to be righteous, Dean responds with "Well, they are righteous. That's kinda the problem." I was surprised by the insight of the writers here. Of course, Dean's logic goes a bit more mainstream by describing the angels as "a-holes who think they are on a holy mission." The Judeo-Christian presentation of angels is anything but cuddly and nice. These beings are portrayed as massively powerful, often causing the humans they visit to fall to their faces (some even pass completely out). Most of their stories include destruction and warfare. The biblical definition of holiness is not friendly and nice and good. In Judeo-Christian belief, the concept of holiness is arguable the most powerful force in the universe. Holiness obliterates all evil and sin and badness from its presence. Angels are holy. This is why Castiel's true form literally burns out people's eyes if they look upon him. While the writers have created their own lore concerning the use of angels in this series, they are sticking quite close to the Judeo-Christian worldview so far.
