Allow me to quote from the Stanford Encyclopedia of Philosophy on the page about intrinsic value, as it's at the heart of moral realism -- I'll not be using RF's quote function for this just so any replies will automatically have it populate so you can refer to it when replying more easily:
"Suppose that someone were to ask you whether it is good to help others in time of need. Unless you suspected some sort of trick, you would answer, “Yes, of course.” If this person were to go on to ask you why acting in this way is good, you might say that it is good to help others in time of need simply because it is good that their needs be satisfied. If you were then asked why it is good that people's needs be satisfied, you might be puzzled. You might be inclined to say, “It just is.” Or you might accept the legitimacy of the question and say that it is good that people's needs be satisfied because this brings them pleasure. But then, of course, your interlocutor could ask once again, “What's good about that?” Perhaps at this point you would answer, “It just is good that people be pleased,” and thus put an end to this line of questioning. Or perhaps you would again seek to explain the fact that it is good that people be pleased in terms of something else that you take to be good.
At some point, though, you would have to put an end to the questions, not because you would have grown tired of them (though that is a distinct possibility), but because you would be forced to recognize that, if one thing derives its goodness from some other thing, which derives its goodness from yet a third thing, and so on, there must come a point at which you reach something whose goodness is not derivative in this way, something that “just is” good in its own right, something whose goodness is the source of, and thus explains, the goodness to be found in all the other things that precede it on the list. It is at this point that you will have arrived at intrinsic goodness (cf. Aristotle, Nicomachean Ethics, 1094a). That which is intrinsically good is nonderivatively good; it is good for its own sake."
The moral realist is explicitly making the argument that some things have intrinsic value -- something that has value "in its own sake" -- rather than extrinsic value, which is value that we minds place onto things.
So the answer to a question like this:
Is that yes, we get a sort of truth out of hypothetical imperatives: it is true that if we value altruism, then we ought not to punch babies. We've established X is moral, in 9-10ths_Penguin's words. But moral realism is about more than just establishing we can make truth statements about things related to morality. It's about WHY we're able to.
The realist would say it's because targets of altruism have an intrinsic value that isn't assigned by other minds; a value that just is mind-externally. For instance, a moral realist would say that even if humanity evolved under different circumstances such that we had different shared moral feelings because of the circumstances of evolution, that it wouldn't matter what our shared moral feelings are: there exists some concrete, objective standard of moral truths that are true regardless of whether we intuit them or not.
Does that help clear up anything? Sorry, I just sort of tagged all the similar questions in one response.
