Truly good characters make truly bad role models.
As those of you who have read my work may well have noticed, I don't really like unambiguously good characters much. There are plenty of unambiguously good characters in other works that I do love, but as a general rule if you were writing a character with the intention of having them appeal to me, I would always advise you to throw in some moral ambiguity.
And I think I finally understand why: Unambiguously good characters are difficult to make symapthetic and not annoying, because sympathy relies on an ability to relate to the character. Relating to a character usually means being able to understand what it would be like to be them, and that gets harder to do the more obviously better than you the character is. It's hard to root for someone when you're aware that they're making you look bad.
Which eventually leads me to my point: People keep trying to include morally-perfect characters in works of fiction to act as 'role models'. It's particularly bad in children's fiction, but basically any genre whose purpose is at least partially thought of as being to moralise or proselytise suffers from it (which may be why religious fiction has a reputation for being - C.S. Lewis excepted - not much good). This could hardly be more self-defeating. Good characters - by which I mean really, truly, inherently, morally righteous ones - make bad role models. A role model is, by definition, someone whom people can emulate. You can't emulate perfection.
Consider a situation wherein your aim is to get to the other side of a wall. Unable to work out how to do it on your own, you decide to call a friend to ask what they would do in your position. For some strange (but no doubt awesome) reason, the only friend in your contacts list is Superman, who replies, "Easy: I'd break it down with my superstrength. Or I'd leap it in a single bound. Hope this helps!"
And then he hangs up.
Superman, in this situation, is setting not a GOOD example, but a very, very BAD one - not because he's showing you a way that doesn't work, but because he's showing you a way that ONLY works if you happen to be as awesome as he is. "Thanks a lot, Superman," you mutter into the phone, not even caring that he's already hung up, "except I'M NOT as strong as you and I CAN'T leap tall buildings in a single bound!"
Creating a 'role model' character who is just an inherently good person results in the same situation. We CAN'T rely on our ability to act as they do, because WE aren't unambiguously good. To be honest with you, every single person I've ever met - including myself - is at least a little bit of a collosal ass. And Mr Role Model doesn't help much in my daily struggle to do what's right, because it's NOT a struggle for him, so at the end of the day we're in two completely different situations in terms of our respective disadvantages and, as such, the same methods will probably not work for both. He doesn't inspire me to resist temptation, or provide insight into how I could make amends after giving in to it, he just makes me envious of his own natural immunity to it.
I should probably point out at this point that you CAN write a character who is 'Unambiguously good' in the sense that they DO get tempted to be evil but never quite give in. And if you successfully pull that off, then the resultant character will probably be less annoying and more sympathetic. They'll also probably be far more tragic (look, for example, at what happened to ol' Jesus Christ after HE made a point of resisting temptation). But this goes back to one of the oldest principles of writing: You can be an exception to every rule, if only you're talented enough. Most of us, though, aren't. That's what makes talent special. Biting off more than we can chew just makes us look WORSE than we are.
In short, WWJD's a good principle to stick to as a sort of hypothetical moral touchpaper test, but if the character being asked that question is even remotely human and relatable (which is necessary to function as a role model), then the literal answer should always be "Not end up in this mess in the first place."
