Ever since Morrowind I haven't liked the Blades, now they are a mere shadow of what they used to be, their time has come to an end, which is made even more obvious by the fact that they try to command the Dragonborn of all people... If it were not for Paarthurnax, Skyrim, hell maybe even Nirn, would not be as it is today to be honest. He is the only one who truly understands the blood that flows through you, the will to dominate and destroy is strong, only through practicing the Way of the Voice are you able to control your abilities, something the Blades could never understand. He has more than atoned for what he did so very long ago. Besides, who are they to judge when they themselves have probably committed atrocities. Hell, even the Dragonborn is no innocent, should he/she be killed too?