I recall a recent posting on List 1 to the effect that Aggadah contains "Hilchot Machshava" or something similar.
And I saw another posting re: v'Ten Tal uMatar on List 2 citing only Talmud and Rambam, ignoring a key Ro"sh on point.
Permit me to address both issues with a single approach.
Re: Aggadah. IMHO one may legitimately dispute or dissent from an Aggadic principle. But first, at least one MUST consult the sources and any relevant literature. Only then may one respectfully disagree.
Similarly with the issue of v'Ten. One may legitimately take issue with the Ro"sh's position, but it is still obligatory to see it and any related Halachic Literature
One is not obligated to always concur with all relevant sources, OTOH one must consult them first and not intentionally ignore them before arriving at a conclusion.