And don't bother telling me that it's worth doing if there's even a tiny chance. The chance is exactly 0, and those resources are better spent on the living.
"We are likely to have life extending and resuscitation technologies in 500 years that are better than what we have today."
and
"The dead rich people in these particular vats of antifreeze have any more than a snowball's chance in hell at being successfully resuscitated."
I think the parent's analysis is correct. Your statements, while also correct, don't really refute the issues pointed out by the parent.
It IS physically possible to revive cryonics patients--as in the laws of physics would permit it, even if we don't have anything near the technology required, yet. This isn't a bold claim but rather a statement of fact with respect to information preservation of the vitrification process, and long-term storage at cryogenic temperatures, both of which are well studied in the context of things like organ donor preservation.
So if you're claiming that cryonics has "a snowball's chance in hell" of working, then I presume that either you are (1) ignorant of the science, or (2) making some sort of statement about long-term storage prospects or the credibility of the organizations involved.
But neither you nor the grandparent actually made any specific claims.
I'm signed up to be a cryonics patient when I die, but yeah, the chances are pretty much nil. Personally, I'll take a slightly diminished bank account and a potentially non-zero percent chance of further life over a zero percent chance, but I won't delude myself into thinking that there's effectively any chance of success here.
Cryonics is ultimately a bet on future technology and future humanity.
Unless you live inordinately long, you'll only be in a position to benefit from that if you are wrong about it being a worthwhile investment. (But right about the technological enablers—just wrong on the socio/legal issues.)
I'd be more concerned with the emotional and mental challenges of being revived centuries hence, which would be considerable to say the least.
Tutankhaman will tell you what to expect when you use cutting-edge technology and preservation techniques in the hopes of some future civilization reviving you.... you'll end up under glass in a Museum. Hell, nobody even TRIED to revive King Tut... you think they'll put much effort into a bunch of anti-freeze saturated popsicles? Seriously doubt it.
That's not a statement of fact, it's a statement of belief. Personally, I think it's highly unlikely that any current vitrification process preserves sufficient information for the patient to be revived. We're nowhere near even understanding what "sufficient information" would be, let alone how to preserve it.
You can flush water pipes with whatever you want and clean and rewater it. A complex organism like the human body - and the brain, we still dont really understand?
Not likely. Maybe not 0 chance in SciFi future, but still not likely.
It's just replacing the faith in one omnipotent's afterlife with another.
You're missing the point though. These solutions entirely rely on future technology development being the omnipotence that gives you afterlife.
To a pre-industrial mind, a cell phone would be magic. Other things that would seem like magic are faster than light travel, perpetual motion machines, or exact quantum state duplicators. However baring radically new and highly unlikely physics (which would be the hugest cop-out to assume), there will never ever be faster-than-light travel, perpetual motion machines, or quantum replicators. Such technology is simply impossible. Not "we don't know how to do it" but "we know that it cannot be done."
Likewise, once your brain is cremated or reduced to worm food, there is absolutely no way to recover that connectome information which defines who you are. The laws of physics disallow it.
I have only the slightest idea of what technology that is able to revive a cryo preserved brain would look like, and it would certainly seem like magic to someone today. But to revive a cremated brain would require actual magic. There's an important difference there.
(That's supposing "information in your brain" would even be sufficient by itself. Another leap of faith.)
Being held in stasis for an unknown length of times seems like utter hell compared to moving on to your next life.
In that sense, a clone is preferable, but maybe not for the new consciousness inhabiting it.