I help Paarthurnax in the end. Why? For the following reasons:
1. Paarthurnax is a http://tvtropes.org/pmwiki/pmwiki.php/Main/RedemptionQuest. If you're a brony or a non-brony who's ever read the fan fic, "Past Sins", the moment you recognized this character trait, you should immediately become a Pro-Paarthurnax person. Of course being a redemption character, if you kill him, you've just proven that redemption means nothing.
2. The Blades do ONE THING. ONE FREAKIN THING. They help you break into the Thalmor embassy. That I can recognize. I love killing Thalmor. But that's it. The Greybeards, let's see what they do. They teach you Unrelenting Force, give you Word Wall locations, and even allows you to hold a Summit Meeting in THEIR TERRITORY.
Let's see what Paarthurnax does for you. He gives you a word for Fire Breath, helps you with finding the Elder Scroll, and helps you teach Dragonrend. Not to mention he lets you be more powerful by giving you some meditation powers.
3. That's not what the Blades are about. The Blades are people who serve the Dragonborn. If the Dragonborn says, "Alright, let's not kill Paarthurnax but let's end Alduin's life," the blades should all rally behind him. No, Delphine is the leader of the Blades. Alright, that much I can accept but still, Delphine needs to realize that they still technically serve the Dragonborn, not her.
Dark: let me get this straight:
Parthurnaax is responsible for butchering many, many, many thousands of innocent men, women, and CHILDREN...thats right...little kids...when he burned down villages and towns, and everything else...and you think its OK that he should be allowed to sit on that mountain top with no consequences for his actions?
Believe it or not, The Dragonborn is doing Parthurnaax "a favor" by killing him....The Dragonborn absorbs Parthurnaax's soul...in essense the Dragonborn "becomes" Parthurnaax in a sense...as Parthurnaax becomes part of him/her....think of it like a Quickening from the Highlander franchise...as we learned early in the game that the Dragonborn and other Dragons can absorb the life essence/knowledge of their slain brethren/dragons....
it is ONLY though the Dragonborn killing Parthurnaax that Parthurnaax can truely be redeemed....by The Dragonborn using Parthurnaax's soul to defeat Alduin and set back the balance....his death also fullfill justice for all those Parthurnaax wrong....again setting the world back to balance...and Parthurnaax finally receives peace from his urge to dominate.
Think of it like this:
In the movie Highlander:Endgame...Connor Macleod kills a pastor(he didn't mean to do it intenionally) him doing this plagued him for centuries...he walked around with a heavy heart...not a day went by Conner did not think about what he had done....He also knew Jacob Kell would catch up to him one day exacting revenge...Connor being afraid to live up to the mistakes of his past dodged Kell for centuries, even went as far as to lock himself up in "The Sancturaly" (akin to Parthurnaax's mountain).....eventually Kell began to kill everyone Conner loved and Conner finally forced his Klansman Duncan MacCleod to kill him and absorb his soul....Duncan was then able to defeat Kell and give Connor his redemption.....The Dragonborn carrying Parthurnaax's Soul is the only way he will ever truely get the Redemption he seeks....and justice and redemption together will be fulfilled and balance will be achieved....
Parthurnaax himself would eventually come to this conclusion o his own(if he truely cares for humans) and would be forced to find another Dragonborn centuries down the road to kill him and carry his spirit to do good deeds knowing his essence was a apart of that.
I know above i was herd on Parthurnaax in my previous post, I just finished killing him...I didn't get any pleasure out of doing it....it made me sad to say good by to Parthurnaax....but it was the "right thing" to do....the right decision is always the hardest, most displeasureable one to make...killing Parthurnaax was displeasurable....but it was the right decision...for everyone involved...besides, the leadership of the Greybeards falls to Agneir now...he is wise in his years, and he can pass Parthurnaax's knowledge down the line of generations....
the bottom line is....justice aside, I would have allowed Parthurnaax to live if i was 100% positive i could trust him...but he himself admits he is not to be trusted...he flat out tells you not to trust him....leaving Parthurnaax alive is a big risk....its not a matter if if Parthurnaax reverts back to his old ways, its a matter of WHEN....and if left alive..when that day comes...I do not want to have that blood on my hands knowing i could have done something to stop it....thats like letting a convicted murderer out of prison on parole against the counsel of those who run the prison, and then that person goes out and does something heinous to somones family member...that sjust a risk i can't afford to take.
The Dragonborn is supposed to be the defender of skyrim...he can't risk that...he just can't...i stand by the Blades...the Blades are right....Parthurnaax is a threat...if left alive one day he WILL turn on humankind...its in his blood...he can't help it...the difference between him and the Dragonborn is the Dragonborn is mortal, Parthurnaax is not...given enough time...and Alduin out of the way....thats just an enabled for Parthurnaax to go back to his old ways...its only a matter of time...i cna't risk him hurting the people of Tamreil in the future...be that future 100 years or 1,000...not if there is something i can do to prevent it...i stand by The Blades!