*shrug*
There are so many different scenario's that contribute to what is an unhappy marriage, especially because you have two people involved and there are a lot of types of abuse, some of which are largely invisible and those are some of the worst.
Obviously, if the two people married cannot even function in the same house, it's better for everyone if they split regardless of who's at fault. This is what I grew up with.
However, I also do think that sticking in an unhappy marriage, even one which is too all outward appearances is functional isn't the answer either and I don't think it's really better for the kids. Kids pick up on these things and learn from these things. Yes, divorce is scary, but growing up and thinking that a "good" marriage includes being quietly miserable isn't really a great thing either.
Ultimately, though, we are looking at this from the wrong side whenever we discuss marriage from the perspective of divorce. I don't think trying to go backwards in how we as a culture deal with divorce is any kind of answer. I think we need to spend more time on promoting good matches to begin with.