gonna go ahead and disagree with a tiny, tiny piece of this -- i don't see natsume as giving people the benefit of the doubt because he wants people to do it for him. nbf always strikes me as a series that's very much about kindness and about understanding the other person's position. natsume tends to assume the best of people either because he's (1) being kind and it doesn't occur to him to be suspicious (see: the tiny mushroom yokai that seriously contemplated feeding him to its friend) or (2) because he wants to be a gentle person. it's not a quid pro quo -- it's entirely focused on what natsume wants himself to be.

mostly i think this makes a difference in the way he reacts to characters that are not super-great -- there's that encounter with matoba at the hakozaki mansion, for example, where natsume walks away thinking not "i don't understand why matoba operates the way he does" but "i just can't bring myself to like exorcists... but perhaps not all of them are like that." he has an opinion and he sticks to it, and i think the number of chances that he gives are limited, if very lenient.

(obv these are just $0.02, op, please do ignore what seems like nitpicking to you!)