Imagine a race of immortals. Nothing can kill them; not disease, old age, etc. They are invincible and they also do not go through the normal aging process of decrepitude of the body and mind associated with mortal aging. If they live forever and these beings are like us in all other ways, they will go through the normal vicissitudes of life, the ups and downs, highs and lows, good times and bad times. So such a life in total will include an infinite positive utility and an infinite negative utility. No matter how good a life one lives, so long as some significant repetition of periods of bad times, they will go through an eternity of suffering as well as good times. Do these times cancel out since both times in bad and in good are infinite in duration? Will such a life ever be worth living if we are to believe that what makes life worth living is experiencing as much good (defined as pleasure or happiness here or "utility") and as few bad (sadness, misery, suffering, etc) as possible? In a finite life, once can experience far fewer bad times than good and vice versa but an infinite life, all experiences, good and bad are equal in amount: both infinite in duration.
Also consider that such an immortal, no matter how virtuous he or she is unless she is perfectly virtuous, will inevitably commit an infinite amount of evil as well as good. Will such evil acts and thoughts be canceled out by her good acts and thoughts? It would appear so as well.
Now consider the human race. If the human race lives on forever (and there is almost no chance of that) then the human race will achieve the same amount of overall collective good and bad. It will achieve (unless it all becomes perfectly virtuous after some period of time continuously) an infinite amount of evil and good collective virtue.
