why does jonas' mother dicourage lily from being a birth mother?

In chapter 3, Lilly suggests she would like to be a birthmother. Mother replies, "Lily!...Don't say that. There's very little honor in that assignment." Birth mothers get treated well while thet are fertile but are put to hard labor once they no longer bear children. Birthmothers are used for systematic reproduction and nothing else. Although Lily's mother does not tell her this, she discourages Lily from even thinking about it.