You come off as assuming that the people in this thread are not aware of the personal identity debate. That doesn't really strike me as productive.

I know the debate exists, I just think the wrong side is winning (in this little corner of the Internet).

These discussions usually occur in an atmosphere where there is far more presumption than there is knowledge, regarding the relationship between the physical brain and elements of personhood like mind, consciousness, or identity.

The default attitude is that a neuron is just a sort of self-healing transistor, that the physical-computational reality in the brain that is relevant for the existence of a person is a set of trillions of physically distinct but causally connected elementary acts of information processing, that the person exists in or alongside these events in some vague way that is not completely specified or understood, and that so long as the cloud of information processing continues in a vaguely similar way, or so long as it is instantiated in a way with vaguely similar causality, the person will continue to exist or will exist again, thanks to the vague and not-understood principle of association that links physical computation and self.

The view of the self which naturally arises subjectively is that it is real and that it persists in time. But because of the computational atomism present in the default attitude (described in the previous paragraph), and also because of MWI dogma and various thought-experiments involving computer programs, the dominant tendency is to say, the natural view is naive and wrong, there's no continuity, you are as much your copies and your duplicates elsewhere in the multiverse as you are this-you, and so on ad infinitum, in a large number of permutations on the theme that you aren't what you think you are or what you appear to be.

Another reason that people are willing to sacrifice the natural view wholesale has to do with attachment to the clarity that comes from mathematical, physical, and computational concepts. These concepts also have an empirical side to their attraction, in that science has validated their use to a certain degree. But I think there is also a love of the types of objective thought that we already know how to perform, a love of them for their own sake, even when they do not easily mesh with something we would otherwise consider a reality. An example would be the flow of time. If there were no mathematical physics which treats time as just another sort of space, we would say, of course time passes; it may be a little mysterious, a little hard to describe (see St Augustine), but of course it's real. But since we have geometric models of space-time which are most easily apprehended in a timeless or static fashion (as a single self-existent geometric object), the flow of time is relegated to consciousness, subjectivity, illusion, even denied outright.

The matter-of-fact belief in uploading (in the sense that a digital emulation of your brain will be conscious and will be you), in cryonics, and a few of the other less baroque permutations of identity, doesn't necessarily derive from this quasi-platonic absorption in abstract objectivity. It can also come from "thought-experiment common-sense", as in your scenario of a world where cryonics or uploading is already common. But the abstract attachment to certain modes of thought is a significant factor in this particular intellectual environment, and in discussions where there is an attempt to think about these matters from first principles. And apparently it needs to be pointed out that everything which is "subjective", and which presents a problem for the standard picture (by which I mean, the combination of computational atomism and physical ontology), is quickly discarded as unreal or is treated as a problem that will take care of itself somehow, even though the standard picture is incredibly vague regarding how identity, mind, or consciousness relates to the physical and biological description.

I lean in the other direction, because the standard picture is still very vague, and also because subjective appearances have evidential value. We have every reason to look for models of reality in which time is real, the self is real, and so on, rather than bravely biting the naturalistic bullet and asserting that all that stuff is somehow unreal or otherwise ontologically secondary. Last year I suggested here that the exact physical correlate of the self might be a specific, very large irreducible tensor factor in the quantum state of the brain. That wasn't a very popular idea. There's also the idea that the self is a little more mesoscopic than that, and should be identified with a dynamic "functional organization" glued together more by causality than by anything else. I think this idea is a little fuzzy, a little problematic, but it's still superior to the patternist theories according to which physical continuity in space and time has nothing to do with identity; and perhaps you can see that on this theory also, a destructive upload or a cryonic resurrectee isn't you - because you were the particular dynamical process which terminated when you died, and the upload and the cryo-copy are distinct processes, with a definite beginning in time which came long after the end of the earlier process on which they were modeled.

You ask how, in a world where cryonic suspension and mind uploading are commonplace, a person could arrive at the intuition that identity does not persist across these transformations. All it would take is the knowledge that a self is an entity of type X, and that in these transformations, one such entity is destroyed and another created. These questions won't remain unanswered forever, and I see no reason to think that the final answers will be friendly to or consistent with a lax attitude towards personal identity. To be is to be something, and inside appearances already tell us that each of us is one particular thing which persists in time. All that remains is to figure out what that thing is, from the perspective of natural science.