The best pieces are those where a handful of memoir writers talk about the issues involved in writing about people you know—taking and retelling their life's stories in ways that may be objectionable or even just unrecognizable to them. I am especially fond of a quote from Alison Bechdel:
I do feel that I robbed my mother in writing this book. I thought I had her tacit permission to tell the story, but in fact I never asked for it, and she never gave it to me. Now I know that no matter how responsible you try to be in writing about another person, there's something inherently hostile in the act. You're violating their subjectivity. I thought I could write about my family without hurting anyone, but I was wrong. I probably will do it again. And that's just an uncomfortable fact about myself that I have to live with.
There is a certain amorality to authorship—even if I still believe that literature is essentialy a moral enterprise. These are difficult positions to try to reconcile. If you're unwilling to take pieces of other people's lives as if they were your own and use them as raw material, then you're in the wrong business.
Maybe one of the reasons I don't write more is that I still have issues with that.