Suppose we could be frozen at death, to be revived centuries later (perhaps as digital 'uploads') by a society of transhuman immortals. Sound good? Many of the folks at Overcoming Bias have little doubt. I lean in their direction, but rather more tentatively. Maybe some people would benefit from this transition, but I think there's a hidden incoherence in calls for more widespread adoption of cryonics.
The first thing to note is that, from an impersonal perspective, we're not doing the world any favours by populating the future with our primitive 20th(-21st) century minds. (What would they want us for? Anthropological interest? But this then raises the distressing prospect that we will 'awaken' only to live out our second lives in a scientific testing facility, or in some sort of transhuman zoo.) Cryonicists hope to be revived by benevolent transhumans, but assuming future altruists could get more bang for their buck by bringing into existence completely new (and better) minds, benevolence would presumably lead them to do that instead.
So cryonicists must assume that it is better to extend an existing life than to create a new one. Maybe we have special obligations to existing people, such that benefiting them personally takes priority over making the world a better place. So let's consider the question from a personal perspective: would cryonic revival make one better off?
To answer this we need to consider what makes for a good life (i.e. good for the person living it). It's not as though longevity is intrinsically desirable. Living longer is only good insofar as this enables us to live better. Put another way: death is only harmful insofar as our life, by ending then, is worse on the whole than it otherwise would have been.
A life has a kind of narrative structure, and a good one (like any good story) will fit together well. We have various life projects -- from developing a systematic philosophy to helping children develop into autonomous adults -- which give our lives much of their 'meaning' and worth. These projects are extended across time: decades, often, and sometimes an entire lifetime. But they are also typically situated in time, and may not survive one's sudden displacement into a radically different future society. So any would-be cryonicist must ask: "What is it that I really want from life? Could I still pursue it in the transhuman utopia?"
Some might. But many people are (quite reasonably!) wedded to the particularities of their life and situation, and would not welcome such drastic change. They would awaken to world where their central concerns and life projects no longer belong. Such radical discontinuity should concern any reductionist about personal identity. For insofar as this newly awakened person would be enculturated into a new society, acquiring new values and life projects, they are effectively becoming a new and different person. But notice that this completely undermines the only justification for reviving them. If the benefits of revival accrue to a different person, then revival is unjustified: a better new life could be created 'from scratch', so to speak.
So cryonics is (at best) only justified for people whose central concerns and life projects could continue to be fruitfully pursued upon revival in a transhuman society. That won't be everyone. For many, the cryovangelist's promise of a 'new life' may be taken literally: given its radical discontinuity with all that they care about, such a new life would do nothing to improve their (current) life.