People often assume that it is religion that gives value to human life. However, when thinking about what religious teachings really mean to the worth of life, it can be argued that these teachings actually cheapen life.
The value of an eternal life
If life on earth is just a bump in the road to all eternity, then how can it have much value? People only tend to value things that are relatively scarce. If gold was as abundant as water, it would certainly have a lower value than it does now. Since the same applies to everything else, isn’t it logical to apply it to life? With life a limitless resource that can never be exhausted, there is no way to really value it. On the other hand, when people have little time left, they value every second.
Sending people from one life to another
When killing someone is just sending them to another life, the act of killing becomes easier. While a psychotic is not going to care regardless, normal people with a conscious need to justify their deeds when they affect others. By teaching people that death is only a movement to another realm, and that god will sort everything out with divine, perfect, merciful justice, people can find justification in taking life. At the worst, their acts of killing, and all forms of atrocities that have been committed in the name of god, have divine sanction. In less dramatic cases, actions that might bring harm to others can be carried out with the feeling they are not really ending a life.
A higher cause
When religion teaches people they are working for a god, violence becomes easier to justify. What is the value of human life when one is following a higher power? History is full of conflicts in which the combatants were certain god was on their side. If religion gave human life a greater value, it would be natural to expect that wars of religion, if they happened at all, would be less violent than other wars. Instead, these conflicts, including the Crusades, saw some of the worst atrocities.
Ancient people thought it necessary to make many sacrifices to their gods, and this included human sacrifice all too often. If gods gave all life, then returning life to them is easy to justify. While the belief that people need to actively sacrifice to their gods has gone away, the idea that people are deserving of death, and whatever punishment god wants to inflict on their ghosts for all eternity, is still very much alive.
The idea of human sacrifice is the basis of the Abrahamic faiths since Abraham himself is said to have nearly made his son a human sacrifice. It should be remembered that Christianity itself is founded on a human sacrifice (Jesus sacrifice). While it is a sacrifice that god willing made of himself to himself, in essence, it still represents a human sacrifice.
The worship of death
Christianity and Islam can be argued to be a kind of worship of death. This life is simply a brief test. It does not really matter, since everything is focused on what comes after. This devalues the lives people have and makes them less likely to strive to live life to the fullest. In fact, human suffering has long been justified as temporary pain on the road to eternity. There is no need to worry about it since the real life is to come. The most extreme form of this can be seen in people who deliberately choose to live lives in ways that strive to deny as many earthly pleasures as possible.
It is hard to see how human beings could enjoy an existence in which life and everything else is in endless abundance. That would be a monotonous existence lacking the ability to fulfill basic human needs such as a way to find a sense of wonderment or be challenged (see: eternal heaven or hell). People seek out thrills and the sense of danger. That is why people are attracted to everything from amusement park rides to sky diving. There is no way any human mind, in its present form, could enjoy living for all eternity.
Whatever, if anything, awaits people after their deaths, they should value the lives they have now. Because they are fragile and finite, they should be thought of as infinitely precious. When a life is taken, a mind and all that is in it may be gone forever. Live life to its fullest and do your best to make it possible for others to do the same. Treating life as a finite resource increases the preciousness of it.