But I think this is the acme of selfishness. I don't want to be immortal, and I wouldn't want to live in a world with 500-year-old know-it-alls running around "oldsplaining" everything to everyone else.
I have, thankfully, a fairly good chance of dying before that happens.
Is it selfish when a centenarian lives past 100? Is each additional year of life obtained by a centenarian “selfishly” stolen from some hypothetical unborn self?
"Do you want to live longer?"
"Yes"
"OH YOU WANT TO LIVE A MILLION BILLION YEARS?!?!"
There are values in between immortality and ~80 years.
They'll decide when they want to decide. Some might choose to actually live forever, and that's fine. Others will choose a more current-human type lifespan, and that's fine. Some will choose 150, some 300, some 1000, some 10,000. All of those numbers are fine.
> And how will they do it?
There are already humane forms of medical euthanasia performed in progressive places in the world; this question already has answers, and likely more will be developed over time. I don't think it's an important question or issue to discuss, as long as people have legal options.