Less a correction than my suspicion that you were reading British texts on the subject and not American ones.

If I'm wrong please correct me, but from my cursery review of the subject from, say, the 1890s to the 1930s, Americans were really on the cutting edge of Mendelian "weed out" strain of Eugenicist thought and we'd had lesser forms like miscegination laws on the books in some states almost since our founding.
I've been under the impression that most British texts (and for that matter, a lot of quite a number of American texts) were about "hygine" and raising a moral, upstanding, tall, mentally forthright or stable or whatever children and improving the human race through selective "breeding" rather than elimination of bad seeds via sterilization and extermination.