I think the opposite. I believe a lack of control, especially over one's mortality is what leads to a lot of the bad shit that happens in the world. If everyone was guaranteed their health and freedom from the shadow of death we'd probably be a damn site happier and less neurotic.
or freedom from the chains of living. It would be interesting to see how everyone reacts to an instant death switch or ability to set your own death date lower or higher than your natural life expectancy without society having control over it. Not only people want control over their lives but once they get it, they will naturally want to control others.
What if advanced medicine can extend your life beyond your natural life expectancy (maybe even immortality) but you don't want to live that longer?
Why isn't it always a good thing to cure people and prevent them from dying as long as possible, John?
Religion perpetuated the notion that living is inherently better than death despite suffering and we are stuck with it everywhere.
Rationally, is it true that someone can be better off dead?
No. For something to be better, it requires comparison of former with later state. Since you won't exist, there is no state to compare. No one dead can feel sadness. (of course that's relying on there being no after life or reincarnation)
Flip that switch, is it true someone can be better off living?
No. For the same reason, you have to presume continued existence is good since you can't rely on comparing states.
How do you know continued existence will be good or better?
That you can't. You can make a guess based on data relying on hedonism but that's all there is. No one agrees on what good continued existence is either so people in part are using their experience and values to judge which doesn't make sense if you allow individuals to have freedom of deciding their own values and life.
I say, we stop extending life expectancy and focus on cutting off the problems that make existing existence a pain even if for majority, happiness or society outweigh it. There are many useless things people waste their life on currently, why do they need to?