Perhaps I am a pessimist, but I don't see the future turning out well for those who have chosen to cryogenically preserve their bodies.Most cryonicists agree. It's often said that getting cryopreserved is the second-worst thing that can happen to you.
How long does someone have to be dead before you say, "What value is there in reviving the dead and frozen rather than preserving the living?" Is it a valid argument after 5 minutes? A year? 100 years? If it were technologically possible to revive people from the 18th century without significantly taxing our own resources, some organization would probably be doing that right now. And the newly-revived 18th century people would probably try to revive their friends if they could.
Of course cryonics organizations don't just toss heads in dewar flasks and forget about them. If revival becomes feasible, the organizations doing it will probably be the same organizations that have maintained frozen heads for decades.
You say cryonics is an act of faith. Most people sign up not because they're convinced it will work, but because they think the expected value is positive. For someone moderately well-off, even a 3% chance at a much longer life is worth the $120/month that a typical life insurance policy and membership costs. Heck, many medical procedures are more expensive and less likely to benefit. If we were talking about an experimental cancer treatment that cost $80k and had a 5% chance of working, few would reject it due to the price.
Those who sign up are usually convinced by evidence. Which brings me to the question: What evidence would convince you that cryonics is worthwhile?
If scanning electron micrographs of cryopreserved mammal brain tissue showed intact nanostructure, would that convince you? How about reversibly-cryopreserved mammal organs? What if a team of scientists cryopreserved a bit of rat hippocampus, then warmed and re-fused it, and couldn't distinguish the cryopreserved cells from control cells?
These have all been done in the past decade.
Rabbit kidney: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781097/
Rat hippocampus: http://www.21cm.com/pdfs/hippo_published.pdf
As it stands today, cryonics is an act of faith, not science. And you're more than welcome to believe in it, just like any other faith...
I don't think cryonics in its current form is likely to work, but I do think the probability of it working is high enough that it's worth signing up. Does this sound like a faith-based argument? If reasoning combined with scientific journal citations is faith, then call me a zealot.