Why do we want to go on living now? Not really an easy question to answer, I think, and yet (by and large) we do. Assuming we could stay healthy indefinitely, I don't see any reason I'd be any more eager to die at 144 than I am now at 44 ... or 544, or 4,400, or 44,000,000. There is more to experience in this world than any of us could ever know in a million lifetimes. If you posit having to do something terrible like feeding on people to stay alive, I suppose, it's a different matter. But absent that, and the infirmities of age--give me that immortality pill, please!