I object to many of your points, though I express slight agreement with your main thesis (that cryonics is not rational all of the time).

"Weird stuff and ontological confusion: quantum immortality, anthropic reasoning, measure across multiverses, UDTesque 'decision theoretic measure' or 'probability as preference', et cetera, are not well-understood enough to make claims about whether or not you should even care about the number of 'yous' that are living or dying, whatever 'you' think you are."

This argument basically reduces to, once you remove the aura of philosophical sophistication, "we don't really know whether death is bad, so we should worry less about death". This seems to me absurd. For more, read eg. http://yudkowsky.net/other/yehuda .

"If people believe that a technological singularity is imminent, then they may believe that it will happen before they have a significant chance of dying:"

If you assume the median date for Singularity is 2050, Wolfram Alpha says I have a 13% chance of dying before then (cite: http://www.wolframalpha.com/input/?i=life+expectancy+18yo+male), and I'm only eighteen.

"A person might find that more good is done by donating money to organizations like SENS, FHI, or SIAI3 than by spending that money on pursuing a small chance of eternal life."

If you already donate more than 5% of your income or time to one of these organizations, I'll buy that. Otherwise (and this "otherwise" will apply to the vast majority of LW commenters), it's invalid. You can't say "alternative X would be better than Y, therefore we shouldn't do Y" if you're not actually doing X.

"Calling non-cryonauts irrational is not productive nor conducive to fostering a good epistemic atmosphere"

Why? Having a good epistemic atmosphere demands that there be some mechanism for letting people know if they are being irrational. You should be nice about it and not nasty, but if someone isn't signing up for cryonics for a stupid reason, maintaining a high intellectual standard requires that someone or something identify the reason as stupid.

"People will not take a fringe subject more seriously simply because you call them irrational for not seeing it as obvious "

This is true, but maintaining a good epistemic atmosphere and getting people to take what they see as a "fringe subject" seriously are two entirely separate and to some extent mutually exclusive goals. Maintaining high epistemic standards internally requires that you call people on it if you think they are being stupid. Becoming friends with a person who sees you as a kook requires not telling them about every time they're being stupid.

"Likewise, calling people irrational for having kids when they could not afford cryonics for them is extremely unlikely to do any good for anyone."

If people are having kids who they can't afford (cryonics is extremely cheap; someone who can't afford cryonics is unlikely to be able to afford even a moderately comfortable life), it probably is, in fact, a stupid decision. Whether we should tell them that it's a stupid decision is a separate question, but it probably is.

"One easily falls to the trap of thinking that disagreements with other people happen because the others are irrational in simple, obviously flawed ways."

99% of the world's population is disagreeing with us because they are irrational in simple, obviously flawed ways! This is certainly not always the case, but I can't see a credible argument for why it wouldn't be the case a large percentage of the time.