It is true that chances can't just be "non-zero" and be rational, nor simply based on faith, because that's basically Pascal's Wager. However I think my 1-10% gut feeling is something that I could probably be talked out of if it were really arbitrarily low like people keep assuming.
Assuming that probability range, I think selling to ordinary people is pretty defensible at $50k-$500k rates, because we already spend around $5M to avoid accidental deaths via regulatory tradeoffs. If it is lower (0.1% say) and yet still not arbitrarily low, we would then need to restrict to either very rich or very desperate people (where the ratio of marginal utility of life to marginal utility of a dollar differs significantly from the norm). Arbitrarily low chances literally on level with egyptian mummification or worshipping a random god is definitely not something that should be sold to anyone (except as a novelty maybe).
Note also that cryonics storage cost is influenced by economies of scale, so mass-produced cryonics is likely to be a lot less expensive per person than the cost you see on the market today. If you could seriously measure a non-arbitrary 0.01% it wouldn't necessarily be impossible to justify even on the mass market and even to relatively death-complacent people -- it would just have to be very cheap for them. Granted, gut feelings are hard to calibrate well to reality at such extremes (hence lottery tickets) so I'm not going to seriously argue that, I'm just saying this to give you a feel for why I think there's a need for fairly strong counterargument before you can reasonably take the position that cryonics is just innately bad/fraudulent business.
I also anticipate various positive externalities from the cryonics business, such as sooner (eventual) development of suspended animation of the damage-free variety, which has potential to save a lot of lives and spare a lot of suffering. These too should be accounted for as part of a robust criticism.
You can look it this way: life after rewarming can last for hundreds of years, easily a thousand as medical technology will have advanced at that point. People are currently willing to pay $100k in medical bills to extend their life by about one year with 50% chance, which means that the cost is $200k per year.
Cryopreservation also costs about $100k (slightly more in real life I guess, I'm rounding numbers for simplicity).
If cryopreservation has a 1% of success to extend life by 1000 years for $100k, then they will "buy" 1 year for $10k. Of course, you can change the numbers (in any direction), e.g. 100 years of life would come out to $100k per year, still cheaper than what most people are willing to pay today to live slightly longer. The 1% success rate is rather pessimistic, too.
If you take quality of life into consideration, the argument starts to favour cryonics quite heavily (we can assume that life is a lot better in the future thanks to advancement of technology).
Where do you get that? From what little I understand, 1% seems highly optimistic, given how destructive the freezing process is at the moment.
They implicitly claim that not only is the chance non-zero, but that it's large enough to be worth the opportunity cost of actually freezing people. I agree that a non-zero chance seems obvious, but this claim definitely does not, and needs a lot more substantiation than there actually is.