The issue of whether to keep people alive depends on what gives a human value.
Is it their mere existence? I can see a potential apocalypse in which the maximum human life value is achieved but things seem so terrible for the world: Advanced technology comes in the future, robots try to get the maximum human life value because they believe human lives are the most valuable thing ever and try to make more. They put all humans in the matrix and breed them at maximum rate. They begin to selectively breed in order to maintain them at less resources, they genetically modify them until they are rats, or turn single human cells into surviving fully-functional organisms and keep trillions in vats. Human life is precious.
Is it the existence of conscious thought? The bottom line is, if we're temporary consciousnesses, we're screwed because we'll all be gone and the universe will not be any different for our presence; it would be foolish to think our little blip on the timeline would be the most important thing ever to happen if billions of years extend before and after. If we're eternal consciousnesses then the decision to kill someone means nothing.
How about the ability for conscious thought to be with us? If we're temporary, same deal. If we're eternal, it's more likely the ones on "the other side" will be in much larger numbers and will prefer us over there; our numbers pale in comparison. Maybe they don't enjoy it over there as much, but it is all of our eventual fates.
Maybe therein lies the value: ability to enjoy the much more pleasant existence in life compared to existence in death. In that case, we'd still have to get used to our eventual mortality. The single century of life compared to millions of millennia would not likely make all of the time bearable, knowing we'd never get to have those lost joys again. It might make it worse.
I can't think of any reasons people should be alive. Is it God's test for us? God would know all about our natures and would not need to test our properties. We would be able to be aware of our properties in an instant if God so desired.
Is it a diversion from unbearable eternity? Maybe we'll get to be alive multiple times. In that case, if we die, we'll get another chance to have fun, but you shouldn't shut down the game early for no reason? Seems like an acceptable theory to me, but we could just be given mindless maximum pleasure instead.
Maybe we'll be judged for the morality we demonstrate here. But God can know how moral we'll be in any given set of circumstances in our lives. In any given upbringing, how moral we'll be. It might be based on our genetic and material makeup, it might not be, but he'll know regardless the outcome of any of the infinite possibilities without needing to check first.
For those we know for a fact commit a crime and are facing life in prison should be entitled to the death penalty. Our states and nation need income, but we are putting great deals of money into feeding and upkeeping prisoners which are simply syphoning money and resources from our government and giving nothing back in return.