Consider all the lies and half-truths we hear from politicians. Swearing upon the Constitution to uphold what it says keeps the ceremony one in which government stays free of religious entanglement and religion stays free of potential political hypocrisy. Rep. Carson provided a precedent for future office winners of minority religions, be they Muslims, Hindus, Buddhists, Wiccans or Jewish Humanists.
Good thought, but why only for adherents of "minority religions"? After all, by and large it's the majority creed that is trying to entangle religion and government. Presumably, they're the one's who need reminding of what they're swearing to uphold.