Let's suppose your mind is perfectly preserved (in whatever method they choose to use). Let's suppose you retain the continuity of your memories and you still feel you are "you." Let's suppose the future society is kinder, nicer, less wasteful, more tolerant, and every kid owns a puppy. Let's suppose the end of fossil fuels didn't destroy civilization because we were wise enough to have an alternative ready in time. Let's suppose we managed to save the ozone layer and reverse global warming and the world is still a more-or-less pleasant place to live in. Let's suppose the future society has actually competent people in political positions.
Good! But still...
What body do you end up having? Even if the future doctors can clone a whole new, young, strong body from your DNA (and remove all your potential genetic diseases), that doesn't mean you're immortal. Physical destruction of the body (from accidents, natural disasters, etc.) is still a concern. Your new body would still need to have cryonics insurance in case anything happens to it. And there's always the risk of spontaneous mutations that will ruin everything: http://www.nytimes.com/2014/01/05/sunday-review/why-everyone-seems-to-have-cancer.html?_r=0 Even if sharks don't naturally die from aging, the mere fact of them living more years increases the probability that they'll eventually find something that kills them. Digital uploading is no guarantee of immortality either. Hard drives can be damaged and destroyed too. Even after getting used to a billion years of subjective existence, you will never really, really be able to shake off the fear of annihilation from unforeseen causes. Even if you (or any of your future copies, which is no guarantee of continued identity) are one of the few lucky who make it to the end of the universe, you will still die. If a heart attack didn't get you, entropy will. So it really doesn't matter how much of an effort you make. In forty years or forty eons, you will still die. What that means to you will depend on how much you plan to do with that time, but unless we find a way to reboot the universe AND survive the reboot AND find ourselves in an environment where life can survive, the last enemy will still be undefeatable.
I don't follow how this is an argument against cryonics, unless you're talking to someone who really truly believed that cryonics meant a serious chance of actual literal immortality.
(Also, I have seen it alleged that at least one plausible model of the future of the universe has it dying after finite time, but in such a way that an infinite amount of computation can be done before the end. So it's not even entirely obvious you couldn't be subjectively immortal given sufficiently advanced technology. Though I think there have been cosmological discoveries since this model was alleged to be plausible that may undermine its plausibility.)
Background:
On the most recent LessWrong readership survey, I assigned a probability of 0.30 on the cryonics question. I had previously been persuaded to sign up for cryonics by reading the sequences, but this thread and particularly this comment lowered my estimate of the chances of cryonics working considerably. Also relevant from the same thread was ciphergoth's comment:
Based on this, I think there's a substantial chance that there's information out there that would convince me that the folks who dismiss cryonics as pseudoscience are essentially correct, that the right answer to the survey question was epsilon. I've seen what seem like convincing objections to cryonics, and it seems possible that an expanded version of those arguments, with full references and replies to pro-cryonics arguments, would convince me. Or someone could just go to the trouble of showing that a large majority of cryobiologists really do think cryopreserved people are information-theoretically dead.
However, it's not clear to me how well worth my time it is to seek out such information. It seems coming up with decisive information would be hard, especially since e.g. ciphergoth has put a lot of energy into trying to figure out what the experts think about cryonics and come away without a clear answer. And part of the reason I signed up for cryonics in the first place is because it doesn't cost me much: the largest component is the life insurance for funding, only $50 / month.
So I've decided to put a bounty on being persuaded to cancel my cryonics subscription. If no one succeeds in convincing me, it costs me nothing, and if someone does succeed in convincing me the cost is less than the cost of being signed up for cryonics for a year. And yes, I'm aware that providing one-sided financial incentives like this requires me to take the fact that I've done this into account when evaluating anti-cryonics arguments, and apply extra scrutiny to them.
Note that there are several issues that ultimately go in to whether you should sign up for cryonics (the neuroscience / evaluation of current technology, estimate of the probability of a "good" future, various philosophical issues), I anticipate the greatest chance of being persuaded from scientific arguments. In particular, I find questions about personal identity and consciousness of uploads made from preserved brains confusing, but think there are very few people in the world, if any, who are likely to have much chance of getting me un-confused about those issues. The offer is blind to the exact nature of the arguments given, but I mostly foresee being persuaded by the neuroscience arguments.
And of course, I'm happy to listen to people tell me why the anti-cryonics arguments are wrong and I should stay signed up for cryonics. There's just no prize for doing so.