I don't think it is a gaffe; I think that when the sentence is read to the end, including "and the minister is the man who can straighten out that idea", she's making it clear that the idea of "extermination" is a mistaken idea.
When Margaret said "women must have the right to live, love..create..destroy..be lazy..". and that "The most merciful thing a family does to one of its infant members is to destroy it" how ought we in this day and age struggle to grasp what she really meant?'
I mean, it really is difficult, isn't it, to get into the minds of Eugenicists, Nazi's and other, oh, I dunno, let's call them idealistic envelope-pushers. What could she have meant....?