For the sake of argument let's assume the worst case regarding current cryopreservation technology. Assume it does too much damage to work regardless of what future tech is possible. That does not rule out advancements in cryopreservation tech in the near term that permit either a) good enough, or b) perfect preservation of the brain (or the full body for that matter) within our lifetimes, without needing to achieve anything approaching MNT or what you term MBT. So this is an independent variable.
Cryobiology has a solid track record of progress, to the point where reversibly preserving embryos and cellular cultures is routine. Tissue slices (which are easier to load and unload cryoprotectants by immersion) can be preserved with 100% cellular survival rates relative to a control, and vitrification, while usually too toxic, can provide good morphological preservation for whole organs. We've yet to postpone aging in any mammal, except via caloric restriction. Even SENS, which aims to avoid most of the work of unraveling metabolism, is very complex and relies on radical gene therapy and quite a bit of guesswork.
Rabbit kidneys are smaller, which affects the rate cryoprotectants can be loaded and unloaded, and the cooling rate which affects toxicity time. Like the brain, kidneys are heavily vascularized, with the exception of the medula at the center which (according to my understanding) is what usually doesn't (but in some cases does) survive cryopreservation.
Reversible vitrification of major organs is a reasonable prospect within this decade. What about vitrification of whole animals? This is a much more difficult problem. Some organs, such as the kidney and brain, are privileged organs for vitrification because of their high blood flow rate. This allows vitrification chemicals to enter and leave them quickly before there are toxic effects. Most other tissues would not survive the long chemical exposure time required to absorb a sufficient concentration to prevent freezing.
B. G. Wowk, Medical Time Travel
Losing a piece of the brain does not always translate to loss of function, in fact many areas seem to operate independently of each other. It is true that such injuries (when they are survived) can often result in personality changes, such as Phineas Gage who survived with memories intact, but with dramatic personality changes after an iron bar went through his skull. But there is a fairly strong argument that brain function could be restored after losing chunks, by using stem cells, growth factors, scaffoldings, etc. to grow new analogous chunks where they are missing that make you at least approach the functionality of an average person possessing your DNA. Conceivably, chip-based digital or analog prostheses could also be used for the missing bits.
The parts of the brain most likely to survive are the outer layer (cerebrum). The cerebellum is harder to perfuse, so it is comparatively unlikely to survive. Fortunately, the personality and higher functions seem to be in the cerebrum.
MNT or MBT are not all or nothing. "Future technology" may sound hand-wavy, but it is a compact way of describing a very large set of potential technologies, all of which could independently or in conjunction lead to reanimation of a sufficiently well preserved person. Bear in mind that plain-vanilla biology is already something that operates on a molecular level, and accomplishes very sophisticated results, despite having had to evolve without goal or guidance in an environment where fluctuations of temperature, differences in available nutrients, genetic mutations, etc. are constantly placing limits on what can be done reliably enough to be passed on.
To me it seems rather more burdensome than less to doubt future ingenuity to the degree that is necessary to rule out cryonics from working, particularly in cases where the degree of morphological preservation of the brain is high.
Don't get me wrong, I'm not saying that cryonics is a generally bad idea. I'm just saying that, as of today, there are better ways to spend your resources (i.e., money).
It's more complicated than that, even assuming you are more or less right. If I spend money on cryonics now, that makes it more likely to be more obviously worth someone else's while later. If someone else spends money on it later, that makes it more likely for it to have retroactively been worth my while to spend it now. So this would be a classic case of "rational irrationality" -- much like wasting your individual time voting in a popular election, cooperating in the prisoner's dilemma / stag hunt, or one-boxing in Newcomb's Paradox.
Of course there are third options to be explored. As it happens, currently I'm allocating money towards living expenses and paying down my credit cards rather than cryonics, at least temporarily until my finances improve. Nonetheless, I do contribute significant time towards arguing for the cause, something I feel is more valuable than being signed up. One might also simply send a check to the cryobiology researchers, for example.
...let's assume the worst case regarding current cryopreservation technology. Assume it does too much damage to work regardless of what future tech is possible. That does not rule out advancements in cryopreservation tech in the near term... within our lifetimes...
In general, I agree, but I'm not sure about the "within our lifetimes" part. I understand that cryobiology has made progress, but I am not convinced that it's moving fast enough. There's a huge difference between preserving tissue slices or even small organs for a relatively short am...
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: