My son wants to enroll at quack medical academy and study . . .?

. . . and study homeopathy. Myself a scientist (geochemist and geologist) by profession, I told him that homeopathic medicine is quackery, same as crystal 'healing.' He responded that the basis of homeopathy is the same as immunology, namely exposure to trace amounts of a harmful substance to develop resistance or immunity. He's got me there! How should I answer him?