So according to you morality is not only relative..it's subjective. Interesting But in this article I'm pretty sure he was addressing the commonly agreed upon 'most good for the most people' morality. I'd go so far as to say that, that is morality.
Your words have many connotations. 'Subjective' and 'relative' are often misunderstood at the best of times. If you could taboo these, we'd see where any real disagreement lay.
Also, I don't see any more disagreement here. 'Greatest good for the greatest number' is a calculation to be made. If that statement sums up all of ethics, then it is a logical fact, not a physical one. I can't shoot your fact to make it different. We can simply turn the criterion for 'good' into a computation, so that we input physical facts, and it comes out with advice on what to ...
Pigliucci:
http://rationallyspeaking.blogspot.de/2013/01/lesswrong-on-morality-and-logic.html