Good moral relativists and bad moral objectivists

A friend of mine who does not believe in objective moral values sent me a message today and said:

Btw... ever notice how the academics and philosophers who tout moral relativism are, for the most part, pretty harmless people? They might assert nihilistic ideas in published scholarship and in discussions, but in their actual behavior, most of them follow the same moral norms as the rest of us (going back to your idea that it's good that nihilists are inconsistent). Meanwhile, members of Muslim terrorist groups murder and torture civilians like it's going out of style, and they're all CERTAIN that an objective morality exists and that they are following the correct one.

He didn't seem to offer this as an argument against moral objectivism. I got the impression that he just found it ironic. But some people have used this observation as an argument against objective morals, so I wanted to post my response to it. This is what I said:

It is ironic that most moral relativists are fairly decent people, and that most terrorists are moral objectivists. But it's only ironic if you assume that moral objectivism is true. The reason is because only under moral objectivism can you say that relativists are "decent" and terrorists are "bad." It's only ironic if the way relativists typically live really is "good," and the way terrorists behave really is "bad." Think about it. Suppose terrorist really think the way they behave is good, and the relativists are evil because they aren't joining in. They might just as well say, "Well this is exactly what we should expect. We moral objectists are good, but moral relativists are clearly shirking their duty, and they're bad." The only reason you and I see any irony is because we think the terrorists' morality is mistaken. But it can only be mistaken if there is a correct morality. And we both think the morality of the terrorists is mistaken, and the morality of most relativists is correct. That's why we both see irony. It's ironic that the relativists would be correct about morals, and the objectivists would be incorrect.

There was more about morality in those messages, so I might post some of that, too, since I haven't been blogging much and need something to keep this blog active.

Part 2: If theologians disagree, how can we know our interpretation is right?

Part 3: Does widespread disagreement on morality meant that there are no objective morals or that nobody knows what they are?