I watched a very long podcast episode with John Smart and Max Marty
https://www.youtube.com/watch?v=rBhjRzxj6eY
John was diving deep into some topics that most people would struggle with but that he clearly thinks about regularly. Max spent a lot of time trying to pin down how John viewed duplicate minds. This is a source of angst for many people and Max couldn't quite accept that a duplicate would really be him. So I'm going to rephrase it based on some of John's ideas mixed with how I regularly think about it.
First of all, if you preserve memories and then duplicate them into another mind, it's much more than just recorded events from your past. When we talk about memories, we're talking about memories that are episodic, semantic, implicit, emotional, procedural, perceptual, habitual, motivational, interpretive, heuristic, cognitive, somatic, reflexive, social, cultural, identity, contextual, and many other kinds. Max actually accepted that the duplicate would think that it was him, which is a leap that many people can make if they think about it for long enough. Max estimated that 50% of people can accept that.
To finish the thought experiment, you just have to envision a world where we routinely make duplicates for various reasons. Physics says that it should be possible, so it will almost certainly happen. Duplicates will be created for revivals, backups, transportation, multitasking, etc. Now, in such a world where everyone does it and has been doing it for a long time, you will basically get used to the idea. It will be so useful and so enriching that your angst will fall away. This has happened many times in history. People quickly got used to being flung through the air in an aluminum can, not because anyone from the 1800s would have thought that was a good idea, but because it was useful and valuable. We don't cut people wide open and replace organs because we naturally enjoy it, but because it's extremely useful and valuable. It solves problems that cannot be solved any other way. As John was trying to explain, those few who choose not to use duplicates will quickly fall behind like the Amish.
The transition to using duplicates won't happen quickly. It will be a very gradual process that never really has an endpoint. So you could also imagine some intermediate stages. I'll pick a "halfway" point as a scenario. Imagine that we all have complex brain implants. We would do much of our thinking in external hardware which we would find very useful of course. The implants would have been gradually getting better for decades, but we would still die of old age. Many of our memories would be duplicated in this hardware because the memories would get gradually duplicated as we used the implants on a daily basis. Having our memories duplicated in hardware would be very useful because they would get retained permanently instead of fading. They would also be more accessible, better organized, and faster. We would also have lots of memories that would have been shared by loved ones or downloaded from others. It would get to the point where we would have far more memories in hardware than in our biological brains. The definition of memory in this context is extremely broad. In this world where we are halfway to being able to make a duplicate, we would already have most of our memories outside of our biological brains. People in a society like that would have much less resistance to the idea of making a duplicate.
Physics says that both the original and the duplicate are actually the same mind. Resistance to the idea of a duplicate is just another form of vitalism, believing that there is a "life force" distinct from physical laws. People will need to adapt to reality if they want to move forward with the rest of humanity. Many people currently have trouble with this, but as it becomes possible, duplicates will simply be a non-issue because we will all happily go along with it.