"I saw a bright light, and I walked towards it. I saw everyone I ever knew and was overcome with a feeling of peace."
Pretty powerful stuff. I would imagine that's been used to comfort a lot of people nearing the end of their lives. The idea that hearing that kind of verification of their faith can bring peace is all too common. Even from an atheistic perspective, one could be fooled into thinking this is an act of mercy, like when you tell people who don't know you're an atheist that you'll pray for them. But you're actually hurting them.
Ignorance has never nor will ever be blissful. Ignorance brings with it immense fear and uncertainty, and anyone that's ever reflected on the human condition knows well that fear and uncertainty that come from ignorance always results in either sadness or anger. By supporting this kind of sentiment, you're enabling an empty understanding of life and death.
If you're presented with this kind of response from someone trying to keep proselytizing even as someone sits on his or her death bed, and you have the opportunity to help, maybe explain the truth:
When the body is dying, the brain undergoes neurophysiological processes which can present as fascinating experiences. Many people go through a rapid reliving of life events, or a "life flashing before one's eyes"; this results from the firing of neurons in the brain activating memories. Many near-death survivors report a feeling of extreme peace or even ecstasy; this is a result from synchronized neuronal activity, where there's a symmetrical firing of neurons (something normally only seen in seizures). Each of these also can cause an invididual to see the "bright light". Why are neurons firing in such abnormal ways? Hypoxia. As one is dying, generally the bloodflow to the brain decreases, cutting off the brain's supply of oxygen. As the brain shuts down, neurons go from active to inactive, firing off.
Ancient cultures recorded near-death experiences and interpreted them the best they could, applying them to whatever superstitions or religions were present. We don't need that crutch anymore. Perminant death brings unparalleled meaning and significance to the little time we have alive. Allowing people the opportunity to look at life objectively—looking back on a beautiful life instead of looking forward to a religious fantasy—is the ultimate act of mercy.