I always thought the motherhood dialog was actually supposed to be over-the-top and "What the fuck?", as a sign that Sarah is actually, factually rather unhinged. She's not crazy for the reasons most people think she's crazy, but that doesn't mean she's 100% sane. The way everyone is just looking at her like "WTF?" and John even goes so far as to interrupt her and suggest they be "a liiiiittle more positive" would seem to suggest, at least to me, that Sarah's filibustering isn't to be taken straight up.