As a sort-of aside, I honestly don't see a lot of difference between "when I die is fine" and just committing suicide right now. Whatever it is that would stop you from committing suicide should also stop you from wanting to die at any point in the future.

This statement is simply not true in this form. My survival instincts prevent me from committing suicide, but they don't tell me anything about cryonics. On another thread, VijayKrishnan explained this quite clearly:

We are evolutionarily driven to dislike dying and try to postpone it for as long as possible. However I don't think we are particularly hardwired to prefer this form of weird cryonic rebirth over never waking up at all. Given that our general preference to not die has nothing fundamental about it, but is rather a case of us following our evolutionary leanings, what makes it so obvious that cryonic rebirth is a good thing.

One can try to construct a low-complexity formalized approximation to our survival instincts. ("This is how you would feel about it if you were smarter.") I have two issues with this. First, these will not actually be instincts (unless we rewire our brain to make them so). Second, I'm not sure that such a formalization will logically imply cryonics. Here is a sort of counterexample:

On a more abstract level, the important thing about "having a clone in the future" aka survival is that you have the means to influence the future. So in a contrived thought experiment you may objectively prefer choosing "heroic, legendary death that inspires billions" to "long, dull existence", as the former influences the future more. And this formalization/reinterpretation of survival is, of course, in line with what writers and poets like to tell us.