I am of the opinion that anyone who claims their argument is more valid because of their credentials and not because of their argument is not someone worth arguing with. In this case, they seem to think that because of their credentials their argument is more sound than yours. While the process of getting his credentials may have provided him with a certain amount of education on a given topic, the credentials themselves have no bearing on a discussion of this sort. He should be able to leverage that education and use it to provide a stronger / more sound argument than your own and win the argument because he is right (or at least because he debates better than you).