The Dragonguard/Blades were founded to fight and kill dragons to protect the entirety of the mortal races. Even Parthy tells you that in your position, he'd not trust a dragon one bit.
In refusing to take Parthy down, you set yourself apart, though not essencially at cross purposes or againt, the Blades/Dragonguard. At that point, working with you carries more risk than reward.
Do you expect everyone to eat out of your hand?