It's like Russell's Teapot.
If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time.
Like arguing about the existence of a god, it's all just conjecture. I don't have proof that he doesn't exist and Sam doesn't have proof that he does exist. Considering the whole thing about false prophets and all that, you'd have to assume that nobody can say for sure why god requires circumcision. It'd all be "well, maybe because god thinks this" or "no, of course not, it's obviously because god thinks that."