Agreed.
I'm attempting to show that ethics are non-derivable from empirical facts
My claim is that regardless of the source of ethics, there must be a rational way to decide among multiple incompatible ethical systems. Otherwise you can't condemn anyone's actions if they have a sincere belief that God supports them.
Because of the 'ought-is' perplex, atheistic libertarians cannot hold that their belief system is the 'most rational' or 'logical'; so, the claim that Objectivists have 'objective' ethics is spurious. They are relativists, just like secular humanists.
Now, you object to the appeal to G-d (I suppose I should start doing that):
My claim is that regardless of the source of ethics, there must be a rational way to decide among multiple incompatible ethical systems.
And this is reasonable. As I noted in an earlier post, John Paul II passionately believes that faith and reason are eminently compatible (JPII is a former philosophy professor himself).
First of all, no other major world religion has been subjected to the same kind of philosophical rigor that Christianity has. Certainly not Islam (unless you want to end up beheaded). But let's take two issues, abortion and homosexuality.
Abortion is condemned in the earliest Christian writings. In the Didache it is condemned, which is about 100AD, right at the beginning of the Church. Now, at that time the physiology of Galen wasn't even available, and people really had no idea how a child was conceived. In addition, abortion was widely practiced and accepted, as was infanticide. Christians objected to this on what they believed (and I believe) to be the will of G-d and refused to practice infanticide or abortion and condemned it. Many Christian martyrs died for their practice of adopting children that had been exposed to the elements to die.
Medical science has now confirmed that a human being is a unique human being from the moment of conception--possesses a unique genetic code and is a unique person. In George's Clash of Orthodoxies (mentioned above), George quotes one doctor who concedes that medical science proves that the uniqueness of the individual starts at conception and ends at natural death. Finally, many pro-choice philosophers are now having to argue that abortion is "justifiable homicide" because they've lost the larger argument as to when life begins. Thus, reason and science confirm faith and tradition on abortion.
Same thing with homosexuality. Homosexuality was widely practiced in Rome. Christians rejected it and steadily marginalized it, based upon Judeo-Christian teaching. Today, leftists and libertarians have have "no problem" with it. Well, now we know that the average male homosexual lives almost half as long as a married heterosexual man (41 years), have higher rates of drug abuse and alcohol abuse, die of horrific diseases (AIDS, etc) and have a ten times greater likelihood of molesting young boys as heterosexual men have as molesting young girls.
Homosexuality is a grave danger to those who practice it, and to broader society in terms of both corrupting the youth of a society, and in term of softer issues like raising health insurance rates for non-homosexuals. Again, this is another confirmation of Judeo-Christian tradition and teaching, broadly defined.
Now, you could say that there are all kinds of things in the Bible (stories) that you find non-credible, but that's not the point. We're talking about ethical systems here, and I'm saying that reason and empirical observation confirms the Judeo-Christian moral teachings over and over again.
Also, I noted above that much of the ethical system of today's skeptics was formed by...Christianity. The reason that you find the idea of walking into the Superbowl to watch a bunch of gladiators impale and hack each other to pieces with tridents and broadaxes repulsive is that Christians put an end to gladiatorial shows seventeen hundred years ago. That kind of spectacle used to be the most popular thing in the Roman Empire. The Emporers used the shows to keep people happy. If you were a Roman citizen at the time of Christ you'd see nothing wrong with the Arena; it had been around for hundreds of years. You grew up going to it like kids today go to baseball games.
Many Christian martyrs went to their deaths because they would not attend the shows. Eventually Christian Emporers, at the urging of Bishops, ended the shows.I think most people would agree--and you would agree--that stopping this was a good idea. People are the same--physically--today as they were then. But the Christian faith elevated the conciousness of the West to the point that such things are now unthinkable.
Martyrs also went to their deaths standing up against infanticide, abortion, homosexuality, pornography (yes, it was around then), and so on not because they believed life would be better for people seventeen hundred years later, but because they were commanded to do so by G-d.
You say that there needs to be a rational way to decide between multiple ethical systems. Ok...would the world be better off right now if we still had infanticide, gladiatorial shows, rampant homosexuality, and so on and so forth?
So much of this stuff is just right before our eyes.