The flip side to that argument is that right now life is short, and so I try and fit as many wonderful experiences into it as I can. If life were long I could put everything off until tomorrow. And that doesn't sound good to me.
What would happen to religion? Do you choose to continue aging, die, and take your chances with the heaven you've been saying exists, or do you take the new pill, and live forever? If you take the pill, what does that say about your faith in the afterlife?
Do we fear death even more? If I'm going to die in a few decades of old age as my health deteriorates, I might as well enjoy my prime, and take some risks now. If I die, well, no big deal, I was going to die soon enough anyway. If I'm married, 60 years old, and my wife dies, that would be a sad day, but let's not kid ourselves, we're getting old. If your grandma passes away, well, it was her time, she lived a long life.
But, if we live forever, we fear those accidents. If your wife dies in a plane crash age 60, how does that affect you? You might have expected to spend the next ten thousand years together, and she's gone. Do we stop taking these risks? Do I step in a car, or on a plane? I'm willing to take that risk now, but if I knew I could potentially live forever, I wouldn't want to risk dying with so much time still remaining.
Do we enter the world of virtual reality? Why leave my home, I could get hit by lightning, I could get shot walking down the street, hit by a car, or attacked by animals. Why don't I lock myself in an underground bunker facility, and connect to the world through virtual reality? I toss on the goggles, and I enter the VR world where I meet with friends and family, and go on wild adventures, because I can take these risks in the VR world. If I die, I respawn. My body is safe in the bunker, while I pretend to be outside.
If anything, I vote for the simulated reality thing. Its like once you are dead, they should be able to take your brain out and connect it to a simulated paradise which would run forever.
Also, there's a fantastic novel from Bruce Sterling called Holy Fire that is devoted to exploring the tension between living to continue living and living in the moment.
I'll take the time to work through my problems thanks.
You personally might rather live a vastly extended span than spend the time you do have skydiving, parasailing, climbing mountains, and doing whatever it is that allows you to enjoy your life to its fullest for however long you have. But that's a real, legitimate choice, and choosing to take risks and experience everything you can is a perfectly valid choice -- even if there's a very real risk that something will go wrong at some point and you will indeed "die screaming."
Given a longer life, I think we would come up with new ways to motivate ourselves, and new challenges. This isn't an insoluble problem, it's a business opportunity for Tony Robbins.
That said I'm not sure a human being could ever fully escape ennui, so maybe there is some upper limit. I don't think 80 years is even close though.