I dont agree with HumbleGamer at all because the rules text for the instinct doesnt support his/her concept of what the superstition barbarian is.
Regarding CaptainMorgan's interpretation based on the use of the word "accept":
We all read "Willingly accepting the effects of spells, even from your allies is anathema to your instinct" as you needing to resist any spells cast on you, as normally you get two options when a beneficial spell is cast on you: either choose to accept or resist the spell.
I dont think "accept" in this context means acknowledging that the spell will have an effect on others. Because if it did that would mean a superstition barbarian would have to pretend fireballs cast by others won't hurt his allies, otherwise by your definition the barbarian would be "accepting" the effect of a spell.
Quote:
Willingly accepting the effects of magic spells (including from scrolls, wands, and the like), even from your allies, is anathema to your instinct. You can still drink potions and invest and activate most magic items you find, though items that cast spells are subject to the same restrictions as all other spells. If an ally insists on using magic on you despite your unwillingness, and you have no reason to believe they will stop, continuing to travel with that ally of your own free will counts as willingly accepting their spells (as do similar circumstances) and thus is also anathema to your instinct.
Everything in that text is specifically about how magic affects the barbarian, so with the absence of rules even mentioning the ability to cast spells shouldn't that mean that it remains unchanged, working as normal?
(I dont think you should add rules inferred from what you think the superstition barbarian should be thematically, as others may have a different theme in mind and not even the flavor text for the instinct mentions a total inability to utilise spells)