The character of Sylvie is unique among any of the characters we've encountered so far in the sense that she doesn't explore philosophical or coming of age concepts (like Holden, Esther, etc.) but rather embodies some of those concepts herself.
Chapter 8, when Ruth is put in the position to experience Sylvie's world, and the subsequent fallout of that night, forces us to address how we feel about Sylvie--a detached transient-- raising two children. In doing so, Housekeeping forces you to think about your views on the nature of transience in the context of a rather rigidly formed society.
The question of where these transients fit into society, especially into the role of raising kids, is more difficult the more you attack it. On one hand, if children are raised under a strict "Home Ec Teacher" discipline, could this way of life be damaging to those children who are naturally "transient"? And if children are raised under a Sylvie discipline, could this way of life be damaging to those children who will find greatest happiness in order and stability?
Housekeeping might make the case that such questions are irrelevant. Sylvie did, after all, grow to live a transient lifestyle after spending her whole childhood. And Lucille did, after all, escape from Sylvie to find a more stable life. In fact, the grandfather could be another example, running from his childhood stability Iowan homeland. Perhaps, if the nature of transience (or lack of transience) is a natural part of a person (as the novel seems to imply), it doesn't really matter who raises you.
However, someone pointed out in class (I think Coleman) that it's easy to have transient people in a heavily structured world (a world where most people are "stable" or whatever), but it's harder (or impossible) to have structure in a world where most people are transient, because society relies on a vast network of people subscribing to the same set of ideals and such, but transience doesn't. Maybe that's part of where most of our inner uncomfort comes from the idea of Sylvie raising children. But mostly, I think it's because wasps and leaves in the corner and moldy, dripping couches is just kind of gross.
"It's about the immensely resourceful sadness of a certain kind of American, someone who has fallen out of history and is trying to invent a life without assistance of any kind, without even recognizing that there are precedents. It is about a woman who is so far from everyone else that it would be presumptuous to put a name to her frame of mind." -New York Times article on Housekeeping
Does Housekeeping really portray Sylvie (or Sylvie's type of person--a transient) as a sad concept? I suppose the whole letting the soggy couch dry on its own and sweeping leaves into the corner of the house might be there simply to make us go "ARG look at this sad was of living!", but classroom discussion on these subjects was generally much more forgiving and I certainly didn't feel that Housekeeping tried to completely paint transience in a negative light.