It depends on what you believe. If you believe that there is life after death, and it's a better one, then living longer on earth isn't necessarily better. I think if you talked to a lot of people who are actually elderly and actually nearing natural death, some of them would wish for another lifetime's worth of years (if it came with renewed health), but some of them would be ready to move on.
No, it doesn't depend on what you believe, it depends on what is actually true. There is no rational justification for believing things that are not true, so there's no way to effectively argue for them.
In your knee-jerkiness you have missed the point. The point is that people who believe in life after death may not desire to live longer. Regardless of whether there actually is life after death, what people believe about it affects their decisions.
This is probably not the place to argue about the existence of God, but I will say this: your reasoning is circular. "There's no rational justification for it, so it's not true; and since it's not true, there's no rational justification for it." You have made up your mind already, so you don't even realize when you beg the question. In fact, many people do see rational arguments in favor; just because you disagree with them doesn't make them irrational. And your stated arguments are, in fact, irrational.
