I'm torn. Because he himself admits that dragons are hard wired to want to take over and are naturally evil. Even one of the quotes while the game loads is something to that effect. I can't remember it's exact wording, though.
But I really don't want to lose the Greybeards as friends. Just to see what would happen, I killed him and went back to the Greybeards and the main guy, I forget his name, I'm not good with names...he actually started yelling at me and wouldn't even look at me, told me to get out. Me cries!!!!
And when I spoke with the Blades woman, she was like "oh, I knew you wouldn't let us down" and then I find out...there are only two people left in the Blades....what? Well, I decided I didn't want her to push me around so I reloaded a saved game before killing him.
Plus, staying friends with the Greybeards gives you quests where to find new shouts. Keep going back to the main Greybeard guy, his name starts with A..and ask him about a new power word and he'll give you a quest to go find a new one. Aces! That works for me.
Edited by Pineapplerum, 20 November 2011 - 06:44 PM.