The civilization-ending risks are the most worrying from my point of view. Basically, I see a couple of scenarios:
Technology never gets anywhere near the point where we can revive frozen brains. Industrial civilization collapses first through a combination of resource constraints, environmental damage, and devastating wars; most likely, these all happen together and feed off each other. This doesn't immediately cause human extinction, but the probability of a future industrial civilization arising from the ruins is very low, because all the easily-extracted fossil fuels, ores etc. have already gone.
Technology continues to advance to a point where revival is becoming distinctly feasible, but such advanced tech also comes with very high and increasing existential risks. For instance genetically-engineered plagues, molecular nanotechnology used as a weapon, strong but unfriendly AI. There is low probability of avoiding all these risks.
It's a nasty dilemma really, and cryonic revival can only happen if we somehow avoid both horns.
That's on top of a separate concern that cryo as currently practised simply comes too late to avoid truly irreversible brain damage (what is sometimes called "information theoretic death"). If critical information about a person's mind has already been lost before freezing then no future technology, however advanced, can restore that mind. I don't know enough about how minds are stored in brains to answer that concern, but I'm not confident. Freezing immediately on point of bodily death (or shortly before) looks much more likely to work, but it happens to be illegal.
How, precisely, would this happen? We aren't writing sci-fi here. There's dozens of countries on this planet with world class R&D occurring each and every day. The key technology needed to revive frozen brains is the development of nanoscale machine tools that are versatile enough to aid in manufacturing more copies of themselves. This sort of technology would change many industries, and in the short term would give the developers of the tech (assuming they had some means of keeping control of it) enormous economic and military advantages.
a. E
I heard that women are difficult to convince when it comes to signing up for cryo. In mentioning cryonics to a dying person, there seems to be a consensus that it's not going to happen. I encountered a post: Years saved: Cryonics vs VillageReach, which addressed my main objection (that the amount of money spent on cryo may be better spent on saving starving children, especially considering that you could save multiple children for that amount of money with high probability whereas you save only one life with low probability by paying for cryo). Now I'm open to being persuaded.
My first instinct was to go read a lot about cryo, but it dawned on me that there are a lot of people here who will want to convince family members, some of them female, to sign up - and these people may appreciate the opportunity to practice on somebody. It has been argued that "Brilliant and creative minds have explored the argument territory quite thoroughly." but if we already know all of the objections and have working rebuttals for each, why is it still thought of as extra difficult to get through to women? If there were a solution to this, it would not be seen as difficult. There must be something that pro-cryo people need for persuading women that they either haven't figured out or aren't good enough at yet.
So, I decided to offer myself for experiments in attempting to convince a woman to sign up for cryo and took a poll in an open thread to see whether there was interest. I don't claim to be perfectly representative of the female population, but I assume that I will have at least some objections in common with them and that persuading me would still be good practice for anyone planning to convince family members in the future. Having a study on persuading women would be more scientific but how do you come up with hypotheses to test for such a study if you have no actual experience persuading women?
So, here is your opportunity to try whatever methods of persuasion you feel like with no guilt, explore my full list of objections without worrying about it being socially awkward, (I will even share cached religious thoughts, as annoyed as I am that I still have them.), and I will document as many of my impressions and objections as I can before I forget them.
I am putting each objection / impression into a new comment for organization. Also, I have decided to avoid reading anything further on cryo, until/unless it is suggested by one of my persuaders.
Well, have fun getting inside my head.