When considering the wars going on, and threat of the Thalmor, supporting and helping rebuild the Blades might be better than keeping the Greybeards happy. After the MQ the Greybeards go back to being useless and not caring about what goes on in the world below, they don't care who wins the civil war, nor do they seem to care about the Thalmor threat. The Blades on the other hand are mortal enemies of the Thalmor, and rebuilding the Blades can only help in defeating the Thalmor. Also I am not entirely convinced that Paarthurnax is truly 100% reformed, When confronted about the Blades desire to have him killed, Paarthurnax tells you that he is reformed now, but in the same conversation he says that dominating others is the nature of dragons, and that not a day goes by where he is not tempted to return to his old ways. Only through self control and mediation is Paarthurnax able to resist those urges, so what's to say in the future he will never lose control? Specially now that Alduin is out of the picture, and Paarthurnax has taken his place as the eldest dragon.

You don't need to be 100% convinced, it technically shouldn't be that simple, as good character development doesn't make perfect characters. And because your a dragonborn you have the same desires as well the Blades should just give you a quest to kill yourself just in case you get out of hand. (following the Blades logic puts your hero on a http://tvtropes.org/pmwiki/pmwiki.php/Main/JumpingOffTheSlipperySlope condition)

It is quite simple from a story RP standpoint you kill an atoner who just helped prevent genocide twice in countless years or side with a two buggy and illogical characters. (Which has greater impact saving the world or participating in another war) Stopping the civil war would literally involve them taking over Skyrim in terms of power which is exactly opposite to why the graybeards are so respected by both sides. Paarthurnax gave humans their freedom back so jumping in and sorting everything out for them would infringe on that freedom.

The blades are replaceable in their current state as they don't actually exist as an organization so are functionally useless in the grand scheme of things. At least Paarthurnax is going to try to teach the other dragons the way of the voice it's something you might hope would help in the future. If he ever does do a face heel turn then it isn't like he is special in any way like Alduin. (Their "mortal enemies" of logic in reality as they let their dynamic oath get in the way of actually thinking things through properly)

The dialog they use is particularly telling as well (http://i67.photobucket.com/albums/h297/Heresiarchqin/4.jpg) which makes them seem awfully like they are literally saying the to them he has http://tvtropes.org/pmwiki/pmwiki.php/Main/YouHaveOutlivedYourUsefulness (Which is not normal)

You should redefine your question, look at it from another perspective and think over it again:

Are those two fanatics worth it?

I ignored the quest after the first time I saw it in my journal. Paarthurnax is not a dragon to me. He is a valuable friend who helped me and I'm going to repay that dept to him by paying a visit once in a while and talking to him. He sounded very sad when he told you about Numinex (the dragon who was imprisoned in Dragonsreach) who lost his mind and even forgot his own name because of loneliness. Paarthurnax was really happy to talk to you when he first saw you as "it has been a long time since [he] had the pleasure of speech with one of his own kind."

I will not repay him for everything he has done for me by murdering him in cold blood. The Blades say they can't help and "guide" (rather control) me if I don't kill Paarthurnax because of their oaths? Because he has outlived his usefulness? I'm fine with that. I don't need their help. I'd gladly kill them, because from my perspective, they have "outlived their usefulness" as well and they want me to murder a friend. Paarthurnax says none of such things despite he knows about the Blades.

"Is it better to be born good, or overcome your evil nature through great effort?" - Paarthurnax

Oh and hes voiced by Charles Martinet.

You dont have to do the quest to get those items. They are in a room in Sky Ruler Temple.

HE'S A FRIENDLY DRAGON!

FRIENDLY!

Blades svck.

The dragon taught you.

Partially Correct. The items (Blade Armor, Dragonsbane) are available once you enter Sky Haven Temple in a room off to the left, Yes.

However, if you haven't taken them before the Quest to kill Paarthurnax is given, it's considered stealing until/unless you actually kill the dragon.

I believe I found a full set of Blades armor and a Dragonbane blade in the Sky Haven Temple ? Just in a chest to the left of the rooms entrance, directly opposite Alduins Wall

I think, was awhile since I saw it.

EDIT, didn't read till the end, I see its been answered already

After finishing the game, I went down to pick it up since I was carrying too much last time - but even before I got the quest, it was considered stealing.