Until very recently, I tended to think of cryonics as something nutty and tacitly assumed that cryonics organisations were a little shady. These weren't strong beliefs, and I knew that I had no real basis for them, so I would never have tried to argue them to others, but they were my impressions. I blame the anti-cult and anti-scam heuristics identified in the comments by Jonathan Graehl and Pavitra.

Now that I've come here and seen all of you rational people into cryonics, I've looked at the references here and realised that my impressions were wrong. So cryonics is not terribly expensive and might well work; how interesting! And yet, I have no desire to sign up myself.

Why not? I believe that the reason is that, to spout a cliché, I've come to terms with death. There was a time when I found it very attractive to believe religious ideas promising immortality, but once I abandoned those as irrational, I faced the realisation that I was going to die permanently some day. That worried me for a while, but then I got used to it; I no longer desired to live forever. I didn't even desire to live longer than about a century.

And since I no longer desire to live so long, I have no desire to sign up for cryonics. If I hadn't been so ignorant about cryonics when I abandoned my religious hopes for immortality, then I might well have held onto that desire. So arguably, the only reason that I don't want to live into the 4th Millennium is that I was wrong about something in the past. Nevertheless, it's still true that I don't particularly want to live into the 4th Millennium. So I'm glad that cryonics is reasonable, and I'm glad that the people on this site who want it are signing up for it, but it's not something that interests me.

This must be an example of a much broader theme. One wants X but comes to the belief that X is impossible. Then one stops wanting X, which is probably a healthy response when X really is impossible. When it turns out that X is possible after all, one still does not want X.

Anyway, somebody who has gone through this process might see cyronics as threatening because it seems to attack their own rationality. It doesn't bother me, because I know that ultimate values don't have to be justified; I don't want to live forever, and you do, and that's fine on both ends. But for someone who wants to believe that their ultimate values are objectively correct, and perhaps also for someone who still wants deep down to live forever but has been suppressing this, learning that something is possible after all can be threatening.