Cryonics isn't trying to escape death or heaven. It's just the best darn technological form of burial that exists.
I've never been a Christian, so I could be wrong about this, but many Christians I'd met would disagree with you. They believe that if they die -- permanently, without hope of revival -- while being "right with God" (the precise meaning of which varies by sect), then they get to go to Heaven. Going to Heaven has infinite positive utility.
Desecration issues aside, if what the cryonics companies are selling is the real deal, then signing up for cryonics involves being bound to your physical body for a long time, potentially forever. Sure, you might be awakened at some distant point in the future, and there is some positive utility to living more days on this Earth, but this utility is finite.
Thus, the Christian has a choice between going to Heaven ASAP, and attaining an infinite positive utility; or signing up for cryonics and either attaining a finite positive utility (if it works), or keeping his utility unchanged for a long time (if it doesn't). Therefore, it would be irrational for the Christian to sign up for cryonics.
They believe that if they die -- permanently, without hope of revival -- while being "right with God" (the precise meaning of which varies by sect), then they get to go to Heaven.
I don't see where the "permanently" part comes from. It may be the layman's interpretation, but I don't think it's Biblically motivated.
I recall seeing, in one of the AI-boxing discussion threads, a comment to the effect that the first step for EY to get out was to convince the other party to even play the game at all.
It has since then occurred to me that this applies to a lot of my interactions. Many people who know me IRL and know a belief of mine which they do not agree with and do not want to be convinced of often adopt the strategy of not talking with me about it at all. For me to convince one of these people of something, first I have to convince them to talk about it at all.
(Note, I don't think this is because I'm an unpleasant person to converse with. Excuses given are along the lines of "I never win an argument with you" and "you've studied it a lot more than I have, it's an unfair discussion". I don't think I'm claiming anything too outlandish here; average humans are really bad at putting rational arguments together.)
I suppose the general form is: in order to convince someone of a sufficiently alien (to them) P, first you must convince them to seriously think about P. This rule may need to be applied recursively (e.g., "seriously think about P" may require one or more LW rationality techniques).
As a practical example, my parents are very religious. I'd like to convince them to sign up for cryonics. I haven't (yet) come up with an approach that I expect to have a non-negligible chance of success. But the realization that the first goalpost along the way is to get them to seriously engage in the conversation at all simplifies the search space. (Deconversion and training in LW rationality has, of course, the best chance of success--but still a high chance of failing and I judge a failure would probably have a large negative impact on my relationship with my parents in their remaining years. That's why I'd like to convince them of just this one thing.)
I realize that this is a fairly obvious point (an application of this--raising the sanity waterline--is the point behind this entire site!), but I haven't seen this explicitly noted as being a general pattern and now that I note it, I see it everywhere--hence this post.