One of the most powerful arguments in my mind for the atheistic viewpoint is that it makes no sense to think that we have 'souls' that can live separately from our bodies. If we have no souls, it makes the whole "God Hypothesis" pointless, as the main carrots (Heaven) and sticks (Hell) that are so fundamental to most world religions are removed.
Take memory. We know that our brains are used to store our memories. We know that if our brains become damaged or diseased we can lose our memories. As we get older we forget things as our brains shrink. So, when my body dies and my soul leaves it, what will I remember? Will I still have a memory? If so, where is the information stored? If I had Alzheimer's disease when I died, will I get some of my memories back afterwards (like some sort of computer back-up recovery system)?
If my soul does have memory, it implies that there is some kind of ethereal memory system outside of my brain cells, and hence a duplicate of my brain. This would, in fact, make the brain redundant ... and of course then you would not expect to lose any memory when the brain is damaged. In this case, it would seem that the brain is a huge con trick by God as it is buzzing away there, but in fact completely unnecessary!
If, on the other hand, my soul takes no memory with it when it leaves my body, would it really be 'me'? It would have no memory of my past life. If St Peter was to ask me about me life when I got to heaven, I would remember nothing about it, and I wouldn't know the reasons for what I did. The point of departure would carry no memories, and so really there would be no connection between my living self and my soul, and I would have lost my identity.
Anyone who has programmed a computer will be aware of the need for memory of one sort or another in order for the computer to do anything intelligent. You need local 'Registers' to perform many of the most basic logical operations, and you need RAM and ROM to do anything really useful (and of course hard wired circuitry ... but that's another story). Without memory we would be unable to communicate with St Peter in any meaningful way anyway.
I suppose our religious friends could argue that there is some kind of "Heavenly i-Tunes" operating. Our bodies are like i-Phones and our memories are all the tunes on it. As we go through life the memories continually get backed up in the i-Cloud so that when we die (lose our phones) they are recoverable from somewhere. In this case we get ALL our memories back, good and bad, unlike real life where we remember some things and not others due to the limitations of our brains.
And then there's personality. Our personalities are formed by the way our brains are formed, either through the DNA or through life experiences. We know that someone's personality can change through brain damage, and hence the brain determines personality. In other words, it is physiological. The brain determines our behaviour, who we love and don't love etc etc Once my body dies and my soul escapes from it, what personality do I have? None at all? Am I like a computer?
In short, if there IS an afterlife, we would be very different to who we are now, and it makes you wonder if there is any relevance, or any point in believing it. Is it something we want anyway? We won't be sitting there chatting away to our long lost loved ones anyway! Conversation, memory and thought processes will be impossible. It will be like Alzheimers disease squared .. drawn to the ultimate conclusion.
Knowing what we know now about the human brain, it seems unnecessary to invent the concept of the soul. In fact, it is stretching credibility to think that it is even possible.
Most importantly, once we view the afterlife in these terms it makes you wonder whether any of the religions (at least the Abrahamic ones) are of any relevance.
