If you're presenting me with a piece of fiction that you've written, I expect that there will be a certain level of intentionality there. You made it up, after all. All the choices are yours...you made the characters who and how they are for a reason. Right? Please?
For the most part, un-intentioned characters--characters who feel like afterthoughts--are problematic simply because, well I expect that there won't be anything in there that feels like an afterthought. A tight, well-written novel is inherently thought-out.
But then there are times where character feels a bit random and flat, and the problem is bigger, at least for me. This character is the woman who sort of inexplicably loves some guy...a deadbeat or even a former abuser, who also tends to be the main character. And she just makes me go...What? Seriously? Why is this girl such a moron?
Same goes for a main character who just can't BEAT the women off of him. Really? Can't you get across his badassness in a more original, non-80s way?
This is not to say that this isn't something that happens. All the time. Women (and Men) love people who aren't good for them. Men (and women) are irresistible. But if you're putting these things into a novel, they better serve a purpose and feel intentional. Because otherwise I'm just going to think you're some creep misogynist. And no one wants that.