Rebuttal of the rebuttal:

Also, nobody who doesn’t want to live longer would have to, so life extension technology wouldn’t result in immortal depressed people.

Suicide is already effectively illegal. Many easy, painless methods are outlawed or not given to the mentally ill (drugs, guns, assisted suicide). Suicide-attempters are force-treated. There is tremendous social pressure to not commit suicide, including inflicted guilt. (For detailed arguments, just read Sister Y's linked blog.)

Personally, I'm not interested in life-extension until life is actually worth living. Several problems (like the harsh, maybe-even-negative-sum social hierarchy) seem unfixable without a major re-engineering of humanity, so I don't expect it to happen anytime soon, if ever.

Having said that, I don't know how bad life in general is. Maybe some people actually have lives worth living. They can extend their lives if they want. I'm not interested in arguing other people into pessimism, and I have no reference point to understand their preference anyway.

However, I think it's credible that 30% or more don't have worthwhile lives. Having more people alive for longer seems like it will only bring back the Malthusian era much faster.