What if someone has rational reasons for rejecting a belief such as cryonics, but is deliberately using Dark Art rhetoric to talk more convincingly about that belief by associating it with low-status people? You’d class them as irrational when you should class them as unethical.
In this case, it might be (epistemically) correct to class them as irrational (with some probability, etc.), given the information you have about them.
Similarly, if someone draws a card at random from a standard 52-card deck, your degree of credence that it is the seven of diamonds should be 1⁄52 - it wouldn’t be correct to be more confident than that, even if in actuality it IS the seven of diamonds, as this is information you do not have access to.
(ETA: I’m speaking abstractly here—making no comment on rational beliefs about cryonics.)
In other words, this is not entirely correct:
In this case, it might be (epistemically) correct to class them as irrational (with some probability, etc.), given the information you have about them.
Similarly, if someone draws a card at random from a standard 52-card deck, your degree of credence that it is the seven of diamonds should be 1⁄52 - it wouldn’t be correct to be more confident than that, even if in actuality it IS the seven of diamonds, as this is information you do not have access to.
(ETA: I’m speaking abstractly here—making no comment on rational beliefs about cryonics.)