It seems that you are venturing into No true Scotsman territory:
Clearly you can divide any research field in sub-fields and sub-sub-fields. You could even try to argue that nobody is an expert in anything they haven't pubished a scientific paper on (and even then, maybe the paper had multiple authors and Author 1 was not an expert in what Author 2 did, and the referees who did the peer review weren't really experts, and so on...), but I don't think that would lead to a viable concept of expertise.
Realistically, we expect researchers within any relatively self-contained field (such as neurobiology or cryobiology) to understand the general principles and issues of their field well enough to tell potentially viable scientific and technological ideas from fringe stuff unlikely to work and outright crackpottery.
Moreover, we expect scientists to be accurate in estimating the level of their own understanding within their field (or at least err predominantly on the side of underconfidence, as per Dunning–Kruger ). Therefore, when multiple scientists independently make a claim about something within their field, barring evidence to the contrary, it seems fair to assume that they know what they are talking about.
It seems that you are venturing into No true Scotsman territory:
It seems like you're doing exactly the same thing you did before: confusing subsets with their parent sets. A subset of various fields would, I assume, have enough relevant expertise to debunk cryonics; these individuals are, traditionally, distinguished from laymen with PHDs by their arguments.
What I observe, however, is that most people, including those in the referenced fields, have only the vaguest position on cryonics picked up from pop-culture. If you're lucky, something like "th...
In the past, the Cryonics Institute has had a policy that said that they would not accept anyone who is not a member. This has changed. The policy now is that someone who has full legal authority over your body can sign you up after you die. It costs $36,250 to be frozen if you are not signed up, which is more expensive. They also will not do anything until you have been on dry ice for 2 weeks after they have been contacted, so not being a member is more risky.
This is very important news for anyone who is currently cryocrastinating. It means that you can drastically increase your chances of survival without filling out any forms. All you have to do is tell a loved one you want to be frozen upon death, and that you would like them to take responsibility for making sure this happens. This takes literally 30 seconds. Do it now!
This news might also be a reason to not sign up right away, if you think something better (like radical life extension or uploading) will come along in your lifetime. We should discuss this in the comments.
Edit: The general consensus of this discussion is that this is a really bad reason not to sign up for cryonics.