But that doesn't mean you shouldn't be aware of market trends. I was giving feedback on a student's work where the main character is rich. Big house, no need to work, no money worries rich. This worried me. We're in a recession, people are losing their jobs, lots of us have debt...could we sympathise with a main character who didn't have money problems?
Yes, there is a genre of books about rich people swanning about in private jets and jumping onto yachts in the Caribbean, but outside that niche, I think most characters are, well, more like most of us. I may be completely wrong about this - and it's 100% the student's choice on what to do - but my instinct says it's harder to get sympathy going for a character who isn't having at least a bit of squeeze financially.
In Kissing Mr Wrong I thought very carefully about a character who argues against giving money to premature baby units - something which is generally considered 'a good thing' although there are lots of logical reasons why it isn't. He's not the main character though, and I then gave him a personal, emotional, tragic reason behind his logical ones, which the main character is then doubly sympathetic to. But I did - and do - worry about it. He couldn't be too unsympathetic about premature babies or the readers would take against him, and by association, my main character.
But that is, essentially, writing for the market. I'm writing with the majority of my likely readership in mind and I hope they will either agree with his utilitarian views or react as the main character does. But generally I write characters who conform to what I think is the majority viewpoint and I do think about my target readership.
So perhaps I should rephrase it: don't write for the market, but be aware of it.