Okay, so you're not saying "a few thousand-year-old men". You're saying a bunch of old men and a bunch of less old men who happen to practice medicine agreed with them. Therefore, it's not arbitrary. The point is, consensus among a certain group of "thinkers" does not make a concept non-arbitrary. I would like to know how ethics can be "tested" as well. What kind of scientific test can you do to determine a moral truth that is not relative to your experience in the world?
"Tried and true" doesn't apply to ethics. No matter how long a moral construct has been tried, it cannot be determined to be "true." A moral construct is a belief in what ought to be, not what is, so tests cannot determine moral absolutes.
You may think it's arbitrary, and I will respect that belief. However, the only way something can be not arbitrary is if it is determined by God. If you believe in God, then you have a basis for believing in absolutes. If you do not, there is no source you can point to in the world that means what you believe is what ought to be accepted by everyone. It's arbitrary.
What you call quack medicine is a whole lot less deadly than western medicine.