No, that's not very rational. Cryopreservation may have low chances of success, but it's like a billion billion billion times better than just dying (which has zero chance of success). Nobody is claiming that cryopreservation is very probable, but it's a lot better than nothing.
>Now, imagine you are trying to flash freeze an entire body.
I don't think your critique is very relevant, when almost all cryopreservation is only done to the brain, not the whole body.
>Ignoring all the cell death that has been happening for the last hour, how about thawing?
Thawing is not relevant to be discussed at this point, because the bodies will not be thawed using current technology. If the cryopreserved brain has enough information to be reconstructed, it will be done at some point using advanced nanotechnology. Nobody will be thawing brains using 21st century technology.
> I'm not even touching the morals and ethics of companies that are under no obligation to actually do what you paid them to do (since you are dead).
Yes, there are risks. Nobody is claiming that cryopreservation has a very high chance of success. It's a lot better than nothing, though. By the way, thse cryocompanies or organizations tend to be owned and supervised by relatives of the cryopreserved people. These managers also want to get cryopreserved themselves, and want to reconstruct their own relatives. In addition, there's great scientific value of bringing 100 year old people back alive.
By the way, scientists don't refer to the cryopreversation as freezing, they call it vitrification.