DUDE. So much smarts. It's making my brain itch... 
So Castiel did say that some of his bros/sis had already died earlier on in the season, and if the only thing that can kill angels IS an angel, then Castiel's known about this possible betrayal for a while. If this dagger IS a standard issue every-angel's-got-one dagger and not Lucifer's, it would certainly explain some of Castiel's doubt even before Uriel's betrayal came into the mix. Because he would have known that it was angels that were killing other angels. Either that or the dagger is actually Lucifer's and no one's mentioned it yet (for another epi?) Did Castiel even know that demons couldn't kill angels? Maybe that's why the demons wanna break Big L out... pesky angels messing with our apocalypse. Let Lucy (and any angel who chose to follow Uriel) kill 'em. Heehee 
Let's say the weapons are made by angels for angels. I'm wondering, if Lucifer does get released, would be able to kill the angel's with HIS own swordy thingy as well as killing scores of humans with his pinky fringer *gigglesnorts, sry*? Would he still have it, since he was an angel before he fell? Or did he somehow become just a demon downstairs? Is SPN the best show on TV?
Clue: yes.
