It's like saying that the future is exactly like the past. (Which is true when applied to the question of non-existence, because what did not exist will cease to exist or continue to be non-existent.)
But that is only true of things which do not come into existence, no? I can safely say I did not exist a thousand years ago, nor will I exist in a thousand years. Further, I can say that from my point of death on, I am non-existent. Similarly, before my birth, I was non-existent.
However, my state of non-existence ended at my birth. Just as my state of existence will end at my death.
In this regard, the future is not exactly like the past. In the past, there was never a time in which I came into existence. In the future, there was a time where I came into existence. Neither of those statements transfer between past and future.
>I can safely say I did not exist a thousand years ago...
I'm not sure of that, yet. We haven't managed to pin down what "I" is or even what "existence" is. I'm thinking in the "we virtualized a copy of your brain" sense - just what is consciousness?
Indeed, the very existence (and non-existence) could be relative - just like time and space. For example, in one frame of reference there may exist a magnetic field while in the other there may be none.
This is "memory", or "trace". Their existence take away from your non-existence, making it incomplete (imperfect), which indeed makes one's future different from one's past.
However, my state of non-existence ended at my birth. Just as my state of existence will end at my death.
In this regard, the future is not exactly like the past. In the past, there was never a time in which I came into existence. In the future, there was a time where I came into existence. Neither of those statements transfer between past and future.