Like, the whole 'fear' thing being the basis of Batman. Bullshit.
The ideal Batman, sure. Know why I liked Dark Knight? The scene on the boats. It was a validation of hope. It was "Bruce does this because he believes in Gotham, and he is right to."
Unfortunately, that's not the Batman who exists in DCU canon. I don't know what the hell that guy's supposed to be about, but he certainly doesn't see the good in people. He can't even bring himself to trust or believe in his own closest allies, be they League or fellow Bats. Guy is all about seeing and anticipating the worst in people. Contingency plans to take down his friends, remember? He's built his whole life philosophy around preparing for the worst, around the firm understanding that people are capable of anything (and by anything, we mean the most depraved and perverse atrocities that would make the Joker flinch).
Clark's the other way. He's trusting and believes the best of people, and it can make him naive; he thought the public wouldn't elect Luthor, and as you mention downthread, trusted Diana here in a way that totally bit him in the ass. Diana left him for last because he was the only one who never even once got a little suspicious. Clark believes people are capable of anything (and by anything, we mean the most profound and exalted miracles that would make Gandhi pause in awe).
And most importantly, both of them are really binary. Think about the way they both treated Diana after "Sacrifice," or the way Bruce acted when they found out Cass had murdered that guy. He rejected it. He wasn't capable of reconciling "Cass, who I know to be Good" with "has committed murder, for any reason." She couldn't have done it, because that would make her Bad. Clark's current treatment of Zod is the same; he can't possibly be doing good, for anybody - that would make him Good, and Clark knows he isn't. Even Bruce's no-kill rule - think about how he presents it. One kill means going over the edge. One kill means giving in to the hatred, to the anger. Hatred and heroism, to his mind, cannot coexist. You must excise, if possible, suppress and deny, if not, any such feelings, because if you acknowledge them, if you let them out, they'll control you, they'll make you Not Good anymore. He cannot allow himself a dark side. Dark sides are what bad guys have.
It's a tremendous denial of reality, to believe that bad thoughts and bad deeds are inextricably linked with bad people, and that to be a good person, you must not have them. It's also one of those things that human beings believe, just as universally and fundamentally as we believe that the sun will come up tomorrow, or that Stuff Like That Can't Happen To Me. Bruce (and Clark) may know intellectually and from experience that all three of those things are not reliable truths, but that doesn't mean they don't still deeply believe them. We are not particularly rational creatures, human beings.