I must agree with
@aheight that pain is necessary and advantageous as a survival mechanism.
Plants don't feel pain. You can tear off a leaf or cut a branch and they won't feel pain. Only the healing process takes place. Why? Because pain would be useless to a plant. It can't run away from the treat nor defend itself. It can only hope the treat will stop before it dies, which is the primary defense mechanism of large trees as it takes a very large treat to kill the tree. For small and fragile plants, the defense mechanism is easy reproduction. It doesn't matter if a plant dies, there are so many other that just begun growing around it.
It could be the same for animals, but the facts is that they feel pain. Why? Because they can run away from danger and/or they can fight back. Pain is the alarm system. For a human, pain is crucial to its survival, as it is not that strong compare to other animal of similar size, it runs relatively slow and the reproductive mechanism to get a «fully operational» individual is probably the worst of all. Keeping the individuals we have alive becomes very important.
Can you imagine if, when someone hit your hand with a hammer, you wouldn't feel pain? Because you wouldn't be bother, you wouldn't take it away and soon you would loose your hand. Pain is necessary and it cannot feel good, otherwise you wouldn't react quickly.
Because of the poor child birth survival rate (and even mother survival), again, pain (emotional pain) came as a savior for the human species. Because a human life is fragile and birth so difficult, the pain suffered by the parents when loosing a child gave them the will to care and protect their offsprings at any cost. If that wouldn't have been the case, there would probably be no humans on this earth. Remember that
we are the only species of the homo genus that survived.
That being said, we might be at a point where we care too much because of this pain which is causing what seems to be overpopulation. A huge drop in population is most likely to happen at one point or another, and it won't change much in the greater scheme of things, even if only a few millions survive. But maybe only the growth will stop and the population will stabilize, maybe we will begin populating other planets. Only time will tell.
As for death, it is also necessary for maintaining life. Life adapts itself to its environment. To do so, it needs to regenerate itself differently as time goes by. Note that I use the word «different» not «better» or «improved». What is right for today may not have been appropriated 10 million years ago and may not be soothed for 10 million years from now.
Many people see living longer as an improvement, but is it? What difference does it really make that someone lives 40 or 80 years? On life's point of view, once an individual of any species has reproduced itself to continue the line, there is no need for it to stay alive. So there is a big difference between a life expectancy of 10 years vs 40 years, but not that much between 80 & 120 years. It is especially true for humans as their fear of living tend to increase as they get older. The more they are aware of their death and the dangers that surround them, the more they live in fear, refusing to make new experiences, letting fear getting control over curiosity. This is completely the opposite of what a child does and it prevents the individuals from adapting to their environment, thus more likelyhood of dying. It is far more easier to create a new individual to begin a new process than to try to save a single one forever.