It's not about the method of discovery but truth-making features. You could look at the mind of a good physicist to determine whether electrons repel each other but that's not what makes "electrons repel each others" true. In contrast, what makes a moral judgment true according to subjectivism is the attitudes of the person who makes the moral judgment.
Do you believe in an objective morality capable of being scientifically investigated (a la Sam Harris *or others*), or are you a moral nihilist/relativist? There seems to be some division on this point. I would have thought Less Wrong to be well in the former camp.
Edit: There seems to be some confusion - when I say "an objective morality capable of being scientifically investigated (a la Sam Harris *or others*)" - I do NOT mean something like a "one true, universal, metaphysical morality for all mind-designs" like the Socratic/Platonic Form of Good or any such nonsense. I just mean something in reality that's mind-independent - in the sense that it is hard-wired, e.g. by evolution, and thus independent/prior to any later knowledge or cognitive content - and thus can be investigated scientifically. It is a definite "is" from which we can make true "ought" statements relative to that "is". See drethelin's comment and my analysis of Clippy.