All of man's efforts at a very fundamental level have been to gain more control over his life and over the environment he lives in. In present times, man can choose when to die but his choice of how long he wishes to live is restricted to a seemingly small range of numbers. Put in a position to choose, I do not believe we'd elect to live for hundreds of years but we'd like to know that we can. Countries do not include nuclear weapons in their arsenal with the intention of blowing up land that does not belong to them at the slightest provocation but they do take comfort from the fact that they can if they wanted to.
Immortality is different from life extension in that aspect. As much as man will want to be able to set the span of his life, he will want to have just as much control over his death. Immortality eliminates control over death. I haven't read enough mythology to understand the concept of immortality and many questions of practicality arise. For one, i assume there would be no suicides, homicides and genocides anymore. However, immortality means that we're not mortals anymore. Will immortal men feel pain? Will a cut on the veins cause one to bleed out to ... what? So the person may not bleed at all or he will continue to live with how much ever blood he has left. Oh, doctors will probably go from owning luxury/ super cars to living in cardboard boxes.
Seeing how the terms of immortality are totally up for speculation and taking into account man's love for control, life extension sounds much more realizable with little no confusion. With the on-going research on telomeres and such, life extension becomes less fantastic and less improbable as decades roll by.
In The Selfish Gene, Richard Dawkins presents an idea as to how the life span of the members belonging to a particular species can be increased by raising the reproductive age; meaning if all women gave birth for the first time after they've turned 40, over several centuries. we may be able to see an increase in the average life span. Genes have no foresight. The survival of any species, among other things, depends on the rate of reproduction. Life Extension now poses a threat to population balance. A very strict code of control would have to be established to control and regulate reproduction.
Extension of life brings with it greater emotional baggage. One will tow more and for a longer duration. Though one may get more opportunities at success, failures will haunt him/ her longer now. Quoting House, "Successes only last until someone screws them up. Failures are forever"
There have been many times when i said, "I wish i had ten lifetimes to try and be good at all the things that interest me." I'm not studying engineering because it is the greatest love of my life. I picked a potential career that held promise, i was good at science and i liked science. I just as easily would have loved to be a dancer, a writer, a florist, a photographer, a fashion designer and a psychologist. These are disciplines that I truly love. Life extension would give people like me the opportunity to explore the breadth and depth of their personality and talents. Then when I have done enough, i can die. It is that simple.
If a debate on life extension should ever arise, I hope one argument no one puts on the table is "This is not natural. So it is not good." I'm royally sick of this sprouting every time someone talks of hormone replacement therapy or genetically engineering for a better fetus. It is essential to understand that the fabric protecting you from the heat and cold does not sprout from the ground; neither does pasta. Going one step backward, we are already extending life by impeding death by surgery and medication to a very good extent. In some sense, life extension is already here; We may not be able to blow life into every dying person but we are making it happen with donor hearts and livers, stem cell therapy and ventilators.
I'm not sure if I ll be around to witness life extension becoming a reality. However, if i were given a choice between exploring a new habitable planet and having my aging halted/ reversed, I'm very sure I'd be excited about the former. I'd definitely go for the latter.