I have no idea what you're trying to do here. Are you presenting your own ideas or are you just playing at being a moral relativist?
I'm trying to do both.
Hence the muddle.
Let me try to separate things.
1) To a believer in the Old Testament god and his Old Testament rules, circumcising your sons is an ethical obligation, because humans have ethical obligations to god.
Or then again, maybe not. If a club has rules that its members are obliged to follow, does that make the club's rules ethical
obligations? For instance, if a social club has a rule that says that members must use the dining facilities at least once a month, does that make eating lunch an ethical obligation?
That strikes me as unlikely. More to the point, would a club member think that a non-club member should also eat at the club at least once a month? That would be simply preposterous, since non-club members are not expected to adhere to the club's rules (indeed, non-club members might be prohibited
from eating at the club, just as a non-Catholic, e.g., is prohibited from participating in many Catholic sacraments).
In the same way, a gentile is not expected to adhere to the rules set down by god in the ten commandments. You say that "humans have an ethical obligation to god," but that's merely a petitio principii
. Clearly, not all
humans have these
ethical obligations to god. If the rules of religion are more like the rules of a closed club than ethical obligations owed to all mankind, then it's clear that only some
humans owe god the duty to obey the ten commandments. And if that's so, then it's also clear that the ten commandments aren't ethical obligations at all, since, as you correctly point out, if they were then that would permit inconsistent systems of morality. As you state:
3) To both me and the believer, the conflict between #1 and #2 means that one of us must be wrong -- because neither of us is a moral relativist.
Rather than maneuver yourself into this corner, isn't it more logical to conclude that you're not talking about ethics at all when you talk about religious obligations?
4) To a moral relativist,the conflict between #1 and #2 means the believer is right given his beliefs, and I am right given my beliefs. It is impossible, and may not even be meaningful, to investigate which one is right.
It's always meaningful to determine if one has made an ethical error.