Rationality is orthogonal to emotions and is not opposed to appeals of emotion for acts with net positive consequences.

Rationality and emotions are not necessarily opposed, but strong emotions can cloud rational judgment.

Cryonics is expecially prone to appeal to emotion, since mortality and group identity ("our tribe") are very powerful sources of emotion. Thus, if you want to keep the discussion about cryonics rational, you should recognize this and try keep the emotional charge as small as possible.

People who propose to spin in the public discourse "poster children" optimized to generate the maximum emotional reaction, are trying to do exactly the opposite, which is a tactic I find intellectually dishonest. Even if you think that cryonics is good for those who sign up, making people sign up for irrational reasons is unethical, in my opinion.

I personally think cryonics is net positive despite the uncertainty and I don't agree with your framing of it as a "questionable practice".

The dictionary definition of questionable is: "open to question or dispute; doubtful or uncertain". If you agree that cryonics has large uncertainty, then you should agree that it is a questionable practice.

I believe the offence derives from you implying or stating that the act of donating was net negative when their evaluation was net positive. Naturally, simply opposing a position is not offensive, but it's rude not to back your point up

I'm not arguing that donating to Suozzi is intrinsically unethical, I'm arguing that donating to Suozzi for PR purposes is unethical. I admit that in my original comment I've used a confrontational tone which might not have been optimal to convey my point, but I stand my point and hope that my position is now clear.