I haven't read the book, but assuming the summary you posted is accurate (a dodgy assumption for a wiki page, I know) it sounds like he's over - stating the extent to which people actually believe - and have believed - in the blank slate and the noble savage. Both ideas have long existed and been discussed in tension with a contradictory notion: the idea of the "noble" savage, for example, did not wholly eclipse the idea of non - noble "savagery," and its counterpart, "civilization." That mode of thought held a place in western thought well into the twentieth century, and is arguably still around today, but referred to obliquely and using different terms. Modern historians and archeologists have also very thoroughly debunked the idea of the noble savage, arguing that indigenous and other hunter - gatherer societies were made up of people who were/are not so different from us. Similarly, the blank slate has long existed in tension with rival views of "human nature" as inhetent, and modern psychologists and neurologists have known for decades that our minds & culture are shaped by a combination of nature and nurture. As a historian of childhood, i can tell you with certainty that the idea of the blank slate has been a contested and controversial one from the begining, and that when you look at actual child rearing practices and theories, ideas of "nature" have always been present and played an important role. So you don't have to look very far or very hard to find evidence that neither of these ideas have been as monolithic or as influential as it sounds like he's claiming they are.

tldr, sounds like he's overstating the extent to which these ideas have shaped our culture and society, and ignoring contradictory ideas and narratives that have been there all along.