Given that ideal reasoners are not supposed to disagree, it seems likely that most if not all of these alternative suggestions can also be explained by their proponents being less than rational.

Please support this statement with any kind of evidence. From where I sit it looks to be simply an error.

As far as I know values do not come from reason, they are a "given" from the point of view of reason. So if I value paper clips and you value thumbtacks, we can be as rational as all get out and still disagree on what we should do.

Further, I think even on matters of "fact," it is not "ideal reasoners" who do not disagree, rather it is reasoners who have agreed on one of a few possible methodologies of reasoning. So I think I have seen the statement, something like "rational bayesians cannot agree to disagree on probability estimates."