I think he makes quite clear that the main argument is that it is not hygienic. In fact his argument that it is an old practice plays into to his hygiene argument. I think what he is saying is that the practice was developed before the germ theory of disease; before people truly knew how disease was spread. With our "updated" knowledge, we should have an "updated" system of greeting. So, though I would usually agree with your point about hating "it's old, ergo it's bad" types of arguments, I don't really think it applies here.