Well I guess I just see it differently. I mean, I understand the argument that you are making, but I would counter with the fact that because Batman isn't an actual person, he hasn't been "affected" by anyone.
The opposite is true: because he is fictional, he has a much more clearly defined history of influences, where with a real person it is much more difficult to determine.
He simply has certain character traits that writers have long ago decided to give him.
It's not that simple. You don't just say "My character is...obsessive!" Not if you know what you're doing, anyway. You have to know
why your character is obsessive, because the why will dictate his responses. Similarly, when you create a supporting character, you do so as a means of affecting your main character.
Sometimes characters are created for very specific purposes. Other times, they wil be created for less important or more general tasks, but you will conceive ways for your characters to interact that you did not anticipate when creating them, and they will
become important.
And in an effort to make the story deeper and more realistic, those same writers have occasionally come up with various other characters as little shill reasons for him to have some of these traits that they originally intended.
You are
vastly underestimating the importance of the supporting cast. You say "in an effort to make the story deeper and more realistic," but you dismiss this as a "fun bonus," when it is in fact of absolute critical importance. If your character simply "is" the way he is, you don't have a character. You've got a sketch. You've got an arbitrary collection of responses that might as well be absolutely random. "Why" is, without question, the most important question behind everything your character does. The supporting cast will always be a considerable portion of the answer.
"Oh Batman should be dark and brooding. Lets um... lets have his parents get killed off when he was a kid, that'll work."
"Oh Batman should never kill the bad guys. Well ... lets have him be close to some morally upstanding people like Alfred and Leslie."
Yes, exactly. If you dismiss that, and simply say "Well, Batman just
is dark and brooding," well, that's just bad writing. Bad, bad, bad. That's a surefire way to make the most flat, uninteresting character you could possibly imagine, and on incomplete one at that--because the question of "why" a character is himself is as critical as who he is in the end. It's all connected, and every change adjusts the way he responds. Batman doesn't like guns because his parents were shot. A writer came up with that idea because his parents were shot. If the parents had been knifed, nobody would have ever come up with the idea that Batman should be adverse to guns. At the very least, the reason behind the aversion would be different, and accordingly his responses to guns would be different.
But this was just a choice on the part of some writers to come up with these reasons, and the reasons don't always agree. Sometimes it's Wayne Senior teaching him the value of life. Sometimes it's Robin pointing it out. Sometimes it's Leslie or Alfred or a girlfriend.
A character can learn the same (or similar) lessons from different people. Why not? I certainly have more than one reason behind my ideals. More importantly, though, is that this is simply the nature of characters who are composites of multiple authors. It's makes the character no less critical.
The only thing that remains consistent is that Batman, as a character, must restrain himself from killing - and whether or not the writers even state a reason for that choice, or if they just said "well this is simply how Batman is" - he would be the same, and act the same way.
The character cannot simply act a certain way "just because." Not unless you want your character to be incomplete and uninteresting.
So Leslie really isn't the source of Batmans pacifism. The source is that a writer needs Batman to retain some degree of pacifism in order to remain in the hero role.
There's no contradiction here. If Leslie is used to that end, that makes her critical--because without her, there's no place for the lessons to come from. If you create a different place, then the character is different for that. The Batman who fights crime because his parents were killed in a drug deal gone bad is different than the Batman who fights crime because his parents were mugged. One is chosen over the other because each will dictate specific responses in the character.
Every choice made serves the character. You don't just say "I'll throw in somebody who teaches batman this and that." You think carefully about who this person is, how Batman relates to them, why he takes what they say to heart--or why he
doesn't. This is how the character is important. Change them, you change Batman. They (and their actions) must be designed specifically to suit your goal. Some other idea will not do the trick.
In the end, you have to know the character. If I want Batman to kill somebody, I can't walk the Joker in and have the Joker say "Killing is good, take this lesson to heart!" I have to decide who Batman will listen to, and why. Under what circumstances will he listen? Perhaps none of the available characters are suitable--perhaps he wouldn't listen to any of them, on this matter. Then I have to create someone new. I have to create the connection that suggests Batman will be affected by them the way I want. Only when I've explained this can I have Batman kill. And, in the future, he will be affected by his actions, and, just as importantly, by what and who
drove him to that action. If I change the reason he killed, I change everything about that part of him--everything about who that event
made him.
Do you understand? I can't say "Batman decides to kill, just because!" No differently, you
cannot say "Batman is obsessive, just because!" You explain why, and then that explanation (be it a character or circumstance) becomes important, because it dictates how you decide the character will respond in the future. Change it, and you change the character.
And if the writer chooses to give further explanation for this essential trait, whether they do it by the shill game of Leslie's words of wisdom or anyone else "affecting him," it's just smoke and mirrors.
All of fiction is smoke and mirrors. This makes nothing any less important.
The character IS the character.
The character is how you build him. Nobody cares about Batman's obsession if you say "Batman is just so very obsessed!" If you have a reason, the reason becomes important by virtue of being the thing that convinced the reader of Batman's obsession. Remove it, and the reader is no longer convinced. Change it, and you have to change the characters specific responses, and you alter who the character is.
Consider this: suppose there is a character who wears a domino mask. A domino mask is much less practical than a full helmet that would protect him, and conceal his identity better. He can't wear a full helmet, though, because he's extremely claustrophobic, and enclosing his head gives him panic attacks.
Now, suppose he needs to wear a helmet in a specific instance. In that instance, unless the writer sucks, he will consider that being forced to wear this helmet is giving him a panic attack and affecting how he acts in this situation. He either manages to subdue his claustrophobia or not, and if he does manage it, even that affects the way he acts. He might be abnormally cautious, for example, and that might affect the outcome of whatever situation he's in. The writer may not have originally intended for him to panic in this part of the book, but it has to has to happen, because that's how the domino mask was explained. If nothing happens and this is not addressed, the reader says "This is stupid," and rightfully so.
Now, suppose this character is adapted to film. They cut out the claustrophobia and say he wears a domino mask because he thinks it's pretty. Suddenly, this character is reckless, driven by superficial leanings instead of practicality, who think prettiness more important than protection. He wasn't reckless in the original version: he wanted to wear a helmet, but he couldn't. In the new version, he says "To hell with protection, I like pretty domino masks!" The character has changed.
Now, when he gets into the situation where he
must where a helmet, everything is perfectly normal. He's not having a panic attack because he's not claustrophobic--wearing a helmet is just a wardrobe change. He does not act abnormally cautious, so the outcome of the situation is not affected. There's been a ripple effect. If you say "He was still cautious, just for a different reason," then you've changed the character. The original character, had he not been having a panic attack, would not have been cautious. The new character, while not having a panic talk,
is cautious. Something must be different between them to make them act differently, so the character has changed again.
Writers first see the character how they want them to be, and then work hard at coming up with reasons "why" that character "is" the way they are.
Yes, and I am explaining to you why they do that: because it's important, for all the reasons I've explained.
You could take all those other made up reasons (characters) out of the equation, and you would still have Batman exactly as he is
For example, look to Joker with or without the origin story. Same crazy bastard
Except, not at all the same. This is what I've been explaining. If you take your character and transplant him onto another background, he will be different in a thousand tiny ways that will culminate in serious and important differences. The Joker who cuts his face is not the same as the Joker who falls in a chemical bath. The Joker who has no origin is not the same as the Joker who has an origin. To say they are the same is superficial. For the writer to write them as if they are the same is simply
bad writing.
I believe I can't put this even more concisely. First, if there is no explanation for why your character is who he is, he will be flat, uninteresting, inconsistent, and worst of all, unconvincing. This is bad. Second, if the explanation changes but the character is not different in some way for the change, this is inconsistent, unconvincing, unrealistic, and pointless. This too, is bad.