I've been thinking about your example of a moral system with the rule that infanticide is permissible. It seems to me that such a "moral system", if such were possible, illustrates why conventionalist, or a moral system by consensus, defining what is right does not really encompass what morality is, and why moral rules are not arbitrary like the rules of baseball.
Aside from the ambiguities of what constitutes "society" (which "society" does one obey?), if society is both the origin and justification of morality, several counterintuitive examples come to mind:
1.If two people lived on an island and shared no society between them one could go over and kill the other on a lark and no moral rule would be violated.
2. If there is no moral law above society, no external standard, there is no basis to criticize or oppose ANY other societies' practices, no matter how repugnant to outsiders those practices might be. Stuffing Jewish people into gas chambers is ok if it's done by consensus.
3. If society is the origin and final measure of morality then all its laws are moral by definition; there can be no such thing as an unjust law.
4. If morality is defined by present society's standard, then any challenge to that standard by a moral reformer would by definition be acting immorally, which seems oxymoronic.
Cordially,
The rules of baseball are hardly arbitrary - they are intended to facilitate the playing of the game. We could certainly imagine, in theory, a rule that allowed pitchers to bean batters without penalty, but in reality, the players (and fans) would never agree to or tolerate such a rule.
1.If two people lived on an island and shared no society between them one could go over and kill the other on a lark and no moral rule would be violated.
In reality, of course, people in such circumstances can be, and are, answerable to a wider society when such acts come to light. This, then, is merely an attempt to redefine "society" in such a way as to avoid the consequences of violating social strictures. It doesn't work, as a practical matter - Vincent Bugliosi once wrote a book about a real case that came about from such circumstances, as a matter of fact.
2. If there is no moral law above society, no external standard, there is no basis to criticize or oppose ANY other societies' practices, no matter how repugnant to outsiders those practices might be. Stuffing Jewish people into gas chambers is ok if it's done by consensus.
"Society" in this case may again consist of a wider set of actors that those immediately at hand. If outsiders object and are in a position to do something about it, the act will not stand.
If, on the other hand, objective moral rules exist and are handed to us by God, but nobody lifts a finger to do something, two million Rwandans will still be just as dead. You can explain to them, I'm sure, how much better off they are with objective, external moral rules, and how much worse things might have been for them if morality existed by consensus.
3. If society is the origin and final measure of morality then all its laws are moral by definition; there can be no such thing as an unjust law.
Sure there is - you just have to do the legwork to persuade others of the injustice of some law in order to see change come about. Which is, of course, exactly what you have to do now. Of course, you may view some law as unjust even in the absence of consensus agreement with your point of view, but you don't get to impose your wishes on everyone else. Which is, of course, exactly how things are now. Obviously, then, this hardly constitutes affirmative evidence in favor of external moral systems - the practical difference is naught.
4. If morality is defined by present society's standard, then any challenge to that standard by a moral reformer would by definition be acting immorally, which seems oxymoronic.
Only if you ignore the context and methods of such challenges. There are plenty of ways in contemporary society to challenge the current standards that are not themselves inherently immoral - they are built into the system itself. If you find some law unjust, you are free to speak out against it to convince others that it should be changed. You are free to work for the election of representatives who will implement the changes you prefer. You are not, however, free to simply ignore the current standards on the basis of your unilateral determination that they are unjust - for that, you will encounter the consequences society has set forth. Nor have you ever been free to do so, under any moral system, of course.