It's fairly straightforward to point out that belief in an afterlife can have the effect of devaluing this life, causing various misconceptions about its purpose, and influencing people to act for the sake of an imagined eternity that will never take place. This much is obvious. But not so much thought has been given to the impact that beliefs in an afterlife have had on the views of atheists. All too often, the repudiation of an afterlife is accompanied by various proclamations about how important it is that we live a limited life and experience genuine death. We see it in the shallow aphorisms claiming that "death gives meaning to life", as though finding a meaning for our lives is only possible if everyone eventually dies. Such a stunning lack of imagination about how to find personal meaning barely deserves the time of day, but it's interesting to consider where this notion might come from.
In many ways, it seems that the recognition that there is no afterlife can lead people to endorse the negation of numerous aspects of that belief. When religious people claim that the prospect of permanent death is nihilistic and renders life hopeless, many atheists reply that this mortality is precisely what gives their lives value. When religious people proclaim the glory of eternal life, atheists instead fear that this would eventually become boring. When religious people are frightened by the reality of actual death, some atheists reassure them that there's nothing to be afraid of, and it'll just be like taking a very long rest - as if they'll even be able to experience a state of restfulness ever again.
But just because an idea is wrong or bad doesn't mean the reverse of that idea must be right or good. If it were that simple, the most ignorant among us could become a source of unparalleled genius, simply by inverting everything they believe. This is clearly no guarantee of rightness or truth, and common atheistic views on death actually end up sharing certain similarities with their religious counterparts. Both religious followers and many atheists ultimately agree that death, whatever its nature, is a good thing that's very important to our lives, and nothing should be done about it. And in both cases, their beliefs serve as a way to cope with something frightening, incomprehensible, and unavoidable, and instead spin it as somehow beneficial to us. It's just another comforting tale to soften the impact of the utter obliteration of human minds.
This is some of the most overlooked damage of belief in an afterlife: simply for the sake of contradicting religion, so many atheists are willing to abandon any desire, let alone effort, toward actual immortality - an immortality born not of supernatural magic, but natural technology. Even after understanding that we exist completely within the natural world, many people still resist any attempt to use that knowledge to do something about the myriad vulnerabilities of our current existence. Sure, science is great for curing diseases and extending lifespans - at a slow enough pace that no one's too uncomfortable about it - but dethroning death itself and eliminating the universal inevitability of our demise is apparently a step too far.
Here we can see how the rightly despised fantasies of religion have thrown the very idea of life without end into disrepute. These hollow, meaningless, imaginary fates have repulsed so many people that when the real thing is finally within our grasp, it's treated as no better than the religious delusions that came before. It takes some effort to work past the well-worn tendency to dismiss the possibility of eternal life, and make it clear that this really is something different. The nonexistence of an afterlife is obvious and trivially easy to recognize, but objections to true immortality end up being much more tenuous.
Our present mortality may influence how we live our lives, but that doesn't mean it must be our only source of purpose. People might say death is what gives meaning to life, but no one is especially eager to optimize for this alleged source of value by seeking to bring about more and earlier death for everyone. After all, if this life is really so important, then why should we have less of it when we could have so much more? Why not seek out the most joy, the most love, and the most discovery we can possibly achieve? Why not enjoy life as much as we can, for as long as we can? And why should this ever have to end? It doesn't - if you're ready to do something about it.