I think (A) is wrong due to false comparison, but I'm not sure that is what tommywallach said.
The false comparison, seems to me, is while the child psychologists are comparing self-esteem in the same child, the author is, however, comparing self-esteem in different children.
The psychologists say that practice will damage the children's self-esteem and make them less confident as adults. It is comparing the "before and after" of using that practice, in the same child.
However, the author is comparing children who are raised and who are not raised under that practice. He is comparing two different groups of children. They are not the same thing. The psychologists can refute him by saying: but if those children weren't put under that practice, they would have become more confident today!