THIS IS USEFUL ADVICE:
If you’ve ever felt like you’re stuck in a writing rut because your characters are blending together, the conflict has stalled, or you're just not sure how to show a character's true colors, your psychological makeup may be getting in your story’s way.
Put simply, stories need conflict, and to make that conflict convincing the writer must be able to see why two people would wholeheartedly believe completely different things.
Meanwhile, the writer's psyche is doing what human psyches do - anything and everything to simplify difficult issues into black-and-white, one-sided terms. The sole purpose of defense mechanisms like denial (ignoring a problem) and rationalization (finding a reason that something not-ok you did is ok) is to keep us in agreement with ourselves.
So how can you make conflict between characters convincing when your psyche is working so hard to keep you from seeing things from multiple perspectives?
Seeing Both Sides
The solution has two parts.
1. Know Yourself
First, Writer, you must know yourself. Only then can you see when you are unintentionally contaminating your characters with your beliefs and attitudes.
2. Know How Your Characters Are Different From Yourself
Second, you must know how your characters are different from yourself - and allow yourself to write about people who believe things that are very different from you, even if it’s a little uncomfortable. (And if you're doing it right, from time to time it should be uncomfortable, because through your antagonist you'll be arguing for something you don't believe.)
Characterization and Conflict: Using Psychological Tests to Improve Your Writing by Carolyn Kaufman, PsyD
SOMEWHAT NECESSARY. Also useful to bear in mind when you're READING something: the author pretty much isn't guaranteed to believe everything the characters say. Now, with this thing I am pretty much consciously contaminating the characters with some of my beliefs - the pro-science stuff in Ben and Hajar and Hana - but I am also not passing that on to every other one of the characters. I feel almost certain this is going to be terminally boring and that no one will read it and blah.
Should I write about that? Does anyone care?