Fair enough. I'm not claiming that there is a supermajority solidly convinced of the practical feasibility of cryonics, and significant life extension, and immortalism. The impression that I get is more nearly that most of the hypotheticals that I see here posit more medical and technical progress than is supported by observation. Now, these are hypotheticals - for instance the discussion of consequences of various (large!) degrees of life extension (starting at 1000-year lifespans) in the responses to the original post on this page. It is perfectly valid to discuss improbable hypotheticals. Nonetheless, I get the impression that very few of the hypotheticals explored on LW posit something close to the stagnation that we've actually seen in many fields. Perhaps it doesn't count as a tribal belief, but it does seem to set a tone of the discussion here - and not in the direction of making the discussion less wrong :-)