This is something that has been bothering me for quite some time. People on these forums, when presented with the argument from absolute morality by theists, generally retreat into moral conventionalism or moral subjectivism. They fall right into the trap of the theists. Moral conventionalism and moral subjectivism are VERY BAD ethical theories.
Here is a typical argument I often see on these forums:
Theist: "Well, if there is no god, then there are no absolute moral standards! Therefore, how can anyone be moral?"
Atheist 1 (conventionalist): "You're right. There are no absolute moral standards-- there are only the standards of society. We are moral because society tells us to be, and we must follow its mores and rules. Those are the standards we live by."
Atheist 2 (subjectivist): "You're right. There are no absolute moral standards-- only individual preference. We live by our feelings and preferences. Those are our moral standards."
Atheist 3 (genetic): "You're wrong. There is a moral standard. We have morals because of genetics. Those are the moral standards we live by."
All of these arguments fail, because they are completely arbitrary. I will attack Atheist 1's argument first:
Atheist 1 gives the conventionalist viewpoint. He believes that society provides moral standards. His argument is essentially this:
P1. Societies have different moral standards, which can change over time.
P2 (implied). The "right thing" is what a society says is right.
C. There are no objective moral standards, because every society has a different set of moral standards.
P2 is clearly false. Consider the same argument, but with "moral standards" replaced with scientific knowledge.
P1. Societies have different scientific knowledge. which can change over time.
P2 (implied). True knowledge is what each society says is scientific knowledge.
C. There is no truth, because every society has a different set of scientific facts.
ie. "In the stone age, people thought the world was flat. Now we think the world is round. Therefore, the world is both round and flat"
or "In ancient greece, they thought slavery was right. In America today, we think slavery is wrong. Therefore, slavery is neither right nor wrong."
The crux is, truth exists independent of a society's view on it. If moral standards existed, then what each society thought of the moral standard would have no bearing on the standard at all. Just because societies have different views on moral standards doesn't mean that objective, absolute moral standards do not exist.
Now I will attack the arguments of atheist 2 and 3.
Atheist 2's argument:
P1. People feel differently about certain actions. Some may like one action, and dislike another and find it repulsive.
P2. What is right is what each person feels is right.
C. There is no objective moral standard, because every person feels differently about different actions.
This argument fails for the same reason that the conventionalist argument fails. We have essentially reduced "society" to "individual," and here we have many different "micro-socieities" each with different standards. However, it is possible that an objective moral standard exists and that some people are simply wrong about them. P2 is false.
Atheist 3's argument:
P1. Genetics influences our feelings and behavior about certain events.
P2. What is right is what genetics tells us to do.
C. There is an objective moral standard, the standard of genetics.
Again, P2 is false. Genes simply affect our behavior, they do not tell us what is right, or what is true. Genetics answers the how and why of moral feelings. Genetics doesn't tell us what we ought to do.
If you believe in any of these ethical theories, I would suggest taking a philosophy or ethics class. The truth is, there is no dichotomy between theistic morality and moral subjectivism or conventionalism. These are not the only ethical theories in the world. There are other, objective, sometimes absolute, moral theories which are much better than any of these. And no, I'm not talking about utilitarianism, which is nearly as flawed as these arguments.