The same desire has appeared in three recent writing classes as well as in the crit group: so many writers I'm encountering want main characters to be sweet or adorable (or both!). They're investing too much into this desire for niceness and not thinking of the consequences to the story. In the case of this draft story by me, the consequences of 'fixing' my main character would have been a complete breakdown in the credibility of the disfunctionality of the family that's at the heart of the tale: you can't have an abusive family and not pay prices for it. Also, a person who is scared is not nice. From inside their head they can look appalling: self-centred; passive; accepting of the unacceptable; full of pain; full of complaints; unable to deal with ordinary events. My tale is too complex for the length, currently, but that's a different matter and I'm working on solving that. I'm not going to change my scared main character.
I do need to think about ways of teaching, however, that the world is not a safe place and that some stories require not-safe character choices. Also, I'm wondering if this reaction I'm seeing so regularly is related to the increase in sexism and racism I'm also encountering. We're supposed to be nice and some people are taking on those values as a way of dealing with the hostile universe (if we're nice then people won't hurt us - I've seen that a lot elsewhere - it's a sort of mantra for dealing with anti-Semitism in some circles - the problems don't diminish but one can hope to be the Jewish best friend whose life the bigot saves) rather than asking "Why?"
It's not readers demanding niceness in this case, nor is it publishers, it's writers. They become unintentionally complicit in repressing conventions for representing anger and difference and challenge.
If we can't make damaged human beings the centre of our stories, then where do the damaged human beings find stories about them and where do we find our cultural narratives for understanding these people and their lives? Where does our society find its healing? How do we all move on from this bad place?
I'm not saying that all characters need to be hurting and damaged and not easy to get on with. I am saying that "I don't like this person" or "I don't want to extrapolate this subject fully because then I'd have to write a damaged person as point-of-view character" are really bad reasons for writing niceness. Targetting specific groups of readers or writing to a specific genre are arguable. Wanting writing to consist of unicorn chasers is not.