I had a lengthy discussion with my father yesterday on the meta-ethics and psychological consequences of believing that there is an eternal post-death existence of some kind where you maintain awareness of who you are. He recognizes the possibility of indefinite lifespans, but maintains that any existence without God's intervention would be finite, and further that a finite existence would be meaningless. Without a belief in God and the infinite lifespan that God can grant, you are forced to conclude that all your actions will become meaningless to you at the moment you cease to exist eternally, since there is no longer a "you" to evaluate the meaning of your actions.
Then he draws the inference that the fact that you will cease to exist at some point means that objectively your life is meaningless, i.e. you can no longer look at the your life from an objective framework and have it be meaningful. He admitted that subjectively you can feel that there is meaning for the intervening time, but to feel a sense of meaning you would have to rationalize away the fact that it is going to end. He contends that such rationalizations are harmful and lead to more short-sighted and/or irrational actions being taken during your lifespan, because there will be a continual conflict between eventually dying and having meaning in your life.
My argument was that a lack of feelings after you are dead is good cause not to take that time period into consideration when considering the objective value of your actions. Even though that state lasts forever, it is a null state and thus shouldn't be taken into consideration when you consider your current (or future) life's meaning and value. It simply is not relevant. Life's meaning and value can be better evaluated from a perspective of either a) value to others (which is actually prone to the same argument, as everyone eventually dying makes your life's actions again pointless at that point in time whenever it comes) and b) value to our future selves, as of any given moment that we actually happen to exist in the future. The second variable is certainly a lot higher if you live longer (and the first if everyone else lives longer, human civilization lasts longer, etc.), but to the degree that you are uncertain of life's continuation beyond a given point you can be uncertain as to exactly how much value there will be.
I do agree with his conclusion that if you try to take into account the whole amount of time you won't exist after you are dead, you have to conclude that life is meaningless as far as self-valuation is concerned, as the infinite timespan of being nonexistent would then outweigh the finite timespan of existing. I simply disagree with the premise that taking that into account is objectively necessary.
There can be a cost associated with uncertainty. In rats, it has been linked to addiction -- a stimulus delivered at regular intervals is not addictive, but at irregular intervals it is. In fact I'd say most irrational behavior is either triggered by or an attempt to avoid uncertainty. The uncertainty factor resulting from removing aging as an absolute cap on lifespan could result in major addictive and compulsive behavior. I just think it is preferable to treat these problems by therapeutic means rather than avoid them by pretending that there is an infinite lifespan awaiting us on the other side (or embracing definite limits on lifespan as deathist humanists do).
The fact that most cryonicists have embraced the right to suicide (while electing to avoid it) may be a way of getting around the uncertainty factor. I can see how having that option available could act as a psychological stabilizer, even if it is not exercised very often. That's not to say I agree with the practice of suicide, but I can see why one would favor its legalization (especially given our growing power to prevent it) and respect the right of individuals to make up their own mind.