Look, I know. First of all this question has been debated countless times. Secondly, it seems the overwhelming opinion is against the murder because paarthy help and go from bad to good and blades mean to me. But I've learned to change my mind about the Civil War because I discovered we were lied to a manipulated by the Thalmor. So now I'm looking more closely into some major moral choices. Well I'd like to count one more and this time for team murder.

We're the prophecied last dragonborn. Alduin's dead in a ditch in nord heaven. The only use for a dragonborn would be to stop another oblivion crisis and we've been doing fine with the medes for hundreds of years. I don't even know if we still have the amulet

So we're the last one who can kill the immortal children of akatosh. Once we're gone, those puppies are IM-MORTAL with a big i. Si stands to reason that the rest of the LDB's life is spent tracking every evil dragon that Alduin brought back

But why kill oversized Mario? Well there's multiple moral reasons. First of all, he himself admits that everyday he's tempted to get back to his evil world domination ways. Being immortal means that this is bound to happen with 100% certainty. It might be a bandit raid that kills argneir and makes him go injustice superman, might not but it's gonna happen.

And that's if he's actually good. Has he really done any good to atone? He was Alduin's right hand man and committed unimaginable atrocities. Then he went into isolation and taught a skill to people who weren't allowed to use it for anything. Sure he helped you kill his old boss when he came back but... Dragons are cunning immortal and therefore patient. P. knew the prophecy, knew Alduin was coming back and knew he would either be a traitor or a second in command. So it is entirely possible and plausible that he helps the LDB, waits for him to die in basically the blink of an eye and then rules the world forever unopposed.

That is a major risk to take for someone who did the bare minimum to help you. Couldn't he gave taken you to sovngard? Help you kill Alduin for good?

Yes you might not like the way the blades treat you but that's a minor downside compared to this and to them this is an obvious choice. And from now on, depending on the role play of my character, it will be a real choice to make.

It is simply too big of a chance to let P-dog outlive us

Tldr : Paarthurnax is immortal, evil and cunning by nature and we're probably the very last dragonborn. He might be playing the long game to rule the world and so maybe has to die if you don't trust him for eternity.

Edit : thanks to everyone who's commenting! I'm learning a lot and loving it!