I understand that there is work supporting the idea that cryonics/regeneration/etc. will eventually be successful. However, I don't feel the need to respond to this work very directly, because this work, after all, is very indirect, in the sense that it is only making plausibility arguments.

In this case, indirect evidence is the only kind of evidence you can hope to obtain, so your current conclusion has to be formed based on indirect evidence. And this applies to any conclusion. If you believe that cryonics won't work, this is also based only on indirect evidence. It has to be.

Now, in most cases, the prior of a given idea not working is high enough, so we have a "by default" argument, believing something is impossible until proven possible. But this is a matter of framing: is it possible to implement a manned expedition to Mars, say? Is it possible to travel faster than light? The difference is always in intuitive estimation of detail that goes into the question, and what exactly is being asked matters. The "impossible by default" heuristic is a good tool, but has apparent points of failure, and you have to be aware of these where obtaining explicit evidence is not expected.

You're saying the level of confidence to look for is one that would be appropriate for any new medical treatment, rather than (say) the confidence you'd look for when making a change in foreign policy.

One reason we're so demanding in the realm of medical evidence is because we can be, and since it can be life and death, if we can be we probably should be. In the case of a pill, we can do an RCT, providing high quality, repeatable statistical evidence on its efficacy - so anyone proposing I take a pill who doesn't have an RCT backing them up is a bit suspicious. In the case of cryonics, I hope it's clear that it's not because of a lack of respect for evidence that we're unable to show you an RCT.

There is absolutely insufficient evidence to have the same confidence in cryonics as we do in, say, ibuprofen for reducing inflammation. Because of this lack of evidence, we have great uncertainty. What we're trying to ask is, in the face of that uncertainty, how will you make a decision? Is it always appropriate in the medical sphere to choose inaction whenever the evidence in favour of action is only weak and circumstantial?

The response to this might be to claim that I am unfairly or erroneously making "demands for particular proof". I think that this point is an intelligent point, but that it is being somewhat abused or overused in this context. In areas like physics or biology, it is completely status-quo to believe nothing except that which has been shown by fairly direct evidence. You might even abstractly characterize the entirety of professional science as an area in which "demands for particular proof" are the centralizing, unifying, distinguishing feature.

That's very much not the case. If one has a hypothesis we don't care which method of bringing evidence for that hypothesis you do as long as it is actual evidence. For example, the neutrino was originally hypothesized based on very indirect evidence. That evidence then became progressively stronger. But at no point did anyone assert that they wouldn't accept neutrinos unless a specific experiment was performed.

Investment and sociological acceptance seem to me separate from the purely physical and biological aspects. For example, I am signaling optimism about the future very strongly by signing up for cryonics. Even an extremely low probability rating for cryonics working would not change this fact.

But in any case, the specific proofs needed for at least some guarded acceptance in physics and biology are already available. We know cells survive in large numbers, memories are structural (not dependent on electric fields), and vitrification limits damage (to the point that a kidney can survive in working condition). If you want to be a scientific skeptic of cryonics you need to be begin as literate of these facts and refer to reasons why you are still skeptical.

The demand for reanimation of a whole human or complex animal is far in excess of what is necessary to prove this as a good bet based on physical and biological data. The cost of ignoring the evidence in favor of cryonics that can accrue before that particular demonstration is vastly disproportionate to the cost of a false positive.