Perhaps Sam can clarify his remarks but that's strongly not what I got from the context. That argument has some validity, but he actually wrote:
How in the world can you assign any value to that proposal? There is a total lack of evidence in support of resurrecting a frozen human because its never been done and as of now nobody knows if it is even possible. So essentially cryonics is a way to spend money on a one in a million chance you might be revived in the future. Why? I would much rather bet on life extension then cryonics.
He didn't say one needs to assign low value to the probability that it will happen but had a problem assigning "any value" due to a "total lack of evidence." That sounds like a much stronger claim especially when he then refers to making a "bet" by comparison on life extension. If that is what Sam meant, I'd be particularly curious what the monetary level would be where he'd sign up.
Incidentally, the claim that because a technology does not yet exist we must assign it a very low probability of arising seems almost trivially false. The largest hard drives today are in the 2-4 terabyte range. I'm pretty willing to bet that we will see 10 terabyte hard drives pretty soon and almost certainly will eventually. The only major ways for this not to happen are a very large scale catastrophe or the discovery of new technologies that render large hard drives unnecessary. Thus, the tiny chance of this not occurring is even smaller if one instead talks about compact data storage objects in the 10 TB range.
One can use other examples which are slightly less trivial. Currently, the best Go programs are in the mid to low dan rankings. But I don't think anyone seriously thinks that because no one has demonstrated a better program that the probability of such programs arising is therefore very low.
The argument type used fails even more badly when one is talking about something like cryonics where we don't even need the technology soon, it just needs to eventually exist.
This argument might be different if Sam focused on technical aspects that would make cryonics difficult in the long-term or if one focused on sociological aspects (which he did briefly touch upon but not in any detail). But the argument being dealt with by my comment seems to focus simply on the claimed lack of "evidence" due to the technology not yet existing. That style argument fails.
Cryonics scales very well. People who argue from the perspective that cryonics is costly are probably not aware of this fact. Even assuming you needed to come up with the lump sum all at once rather than steadily pay into life insurance, the fact is that most people would be able to afford it if most people wanted it. There are some basic physical reasons why this is the case.
So long as you keep the shape constant, for any given container the surface area is based on a square law while the volume is calculated as a cube law. For example with a simple cube shaped object, one side squared times 6 is the surface area; one side cubed is the volume. Spheres, domes, and cylinders are just more efficient variants on this theme. For any constant shape, if volume is multiplied by 1000, surface area only goes up by 100 times.
Surface area is where heat gains entry. Thus if you have a huge container holding cryogenic goods (humans in this case) it costs less per unit volume (human) than is the case with a smaller container that is equally well insulated. A way to understand why this works is to realize that you only have to insulate and cool the outside edge -- the inside does not collect any new heat. In short, by multiplying by a thousand patients, you can have a tenth of the thermal transfer to overcome per patient with no change in r-value.
But you aren't limited to using equal thickness of insulation. You can use thicker insulation, but get a much smaller proportional effect on total surface area when you use bigger container volumes. Imagine the difference between a marble sized freezer and a house-sized freezer. What happens when you add an extra foot of insulation to the surface of each? Surface area is impacted much as diameter is -- i.e. more significantly in the case of the smaller freezer than the larger one. The outer edge of the insulation is where it begins collecting heat. With a truly gigantic freezer, you could add an entire meter (or more) of insulation without it having a significant proportional impact on surface area, compared to how much surface area it already has. (This is one reason cheaper materials can be used to construct large tanks -- they can be applied in thicker layers.)
Another factor to take into account is that liquid nitrogen, the super-cheap coolant used by cryonics facilities around the world, is vastly cheaper (more than a factor of 10) when purchased in huge quantities of several tons. The scaling factors for storage tanks and high-capacity tanker trucks are a big part of the reason for this. CI has used bulk purchasing as a mechanism for getting their prices down to $100 per patient per year for their newer tanks. They are actually storing 3,000 gallons of the stuff and using it slowly over time, which implies there is a boiloff rate associated with the 3,000 gallon tank in addition to the tanks.
The conclusion I get from this is that there is a very strong self-interested case (as well as the altruistic case) to be made for the promotion of megascale cryonics towards the mainstream, as opposed to small independently run units for a few of us die-hard futurists. People who say they won't sign up for cost reasons may actually (if they are sincere) be reachable at a later date. To deal with such people's objections and make sure they remain reachable, it might be smart to get them to agree with some particular hypothetical price point at which they would feel it is justified. In large enough quantities, it is conceivable that indefinite storage costs would be as low as $50 per person, or 50 cents per year.
That is much cheaper than saving a life any other way. Of course there's still the risk that it might not work. However, given a sufficient chance of it working it could still be morally superior to other life saving strategies that cost more money. It also has inherent ecological advantages over other forms of life-saving in that it temporarily reduces the active population, giving the environment a chance to recover and green tech more time to take hold so that they can be supported sustainably and comfortably. And we might consider the advent of life-health extension in the future to be a reason to think it a qualitatively better form of life-saving.
Note: This article only looks directly at cooling energy costs; construction and ongoing maintenance do not necessarily scale as dramatically. The same goes for stabilization (which I view as a separate though indispensable enterprise). Both of these do have obvious scaling factors however. Other issues to consider are defense and reliability. Given the large storage mass involved, preventing temperature fluctuations without being at the exact boiling temperature of LN2 is feasible; it could be both highly failsafe and use the ideal cryonics temperature of -135C rather than the -196C that LN2 boiloff as a temperature regulation mechanism requires. Feel free to raise further issues in the comments.