I can understand what physical conditions you are describing when you say "two rocks". What does it mean, in a concrete and substantive sense, for murder to be "wrong"?
I can give you two answers to this, one which maps better to this community and one which fits better with the virtue ethics tradition.
There exists (in the sense that mathematical functions exist) a utility function labeled 'morality' in which actions labeled 'murder' bring the universe into a state of lower-utility. I make no particular claims about the proper way to choose such a utility function, just that there is one that is properly called 'morality', and moral disputes can be characterized as either disputes over which function to call 'morality' or disputes over what the output of that function would be given certain inputs.
'Good' and 'bad' are always evaluated in terms of effects upon a particular thing; a good hammer is one which optimally pounds in nails, a good horse is fast and strong, and a good human experiences eudaimonia. Murder is the sort of thing that makes one a bad human; it makes one less virtuous and thus less able to experience eudaimonia.
It could be the case that the terms 'good', 'bad', and 'eudaimonia' should be evaluated based on the preferences of an agent. But in that case it that does not make it any less the case that moral facts are facts about the world that one could be wrong about. For instance, if I prefer to live, I should not drink drain cleaner. If I thought it was good to drink drain cleaner, I would be wrong according to my own preferences, and an outside agent with different preferences could tell me I was objectively wrong about what's right for me to do.
As a side note, 'murder' is normative; it is tautologically wrong. Denying wrongness in general denies the existence of murder. It might be better to ask, "What does it mean for a particular sort of killing to be 'wrong'?", or else "What does it mean for a killing to be murder?"
Okay, we don't disagree at all.
There is an objective sense in which actions have consequences. I am always surprised when people seem to think I'm denying this. Science works, there is a concrete and objective reality, and we can with varying degrees of accuracy predict outcomes with empirical study. Zero disagreement from me on that point.
So, we judge consequences of actions with our preferences. One can be empirically incorrect about what consequences an action can have, and if you choose to define "wrong" as those actions which reduce the util...
People who grow up believing certain things,
even if they later stop believing them,
may not quite realize how the beliefs sound to outsiders...
(SCENE: A small cottage in Nazareth.)
Joseph: Mary, my dearest fiancée, there's something I've been meaning to talk to you about.
(Mary's shoulders slump. Slowly, as if under a heavy burden, she turns around to face Joseph.)
Joseph: You seem to be getting fat around the waistline, and throwing up in the morning, and, er, not getting any periods. Which is odd, because it's sort of like -
Mary: Yes! I'm pregnant! All right? I'm PREGNANT!
Joseph: How is that possible?
(Mary's shoulders slump further.) Mary: How do you think?
Joseph: I don't know, that's why I'm asking you. I mean, you're still a virgin, right?
(Mary looks up cautiously, and sees Joseph's face looking blankly puzzled.)
Joseph: Well?
Mary: God did it.
Joseph: You had sex with -
Mary: No! Haha. Of course not. I mean, God just snapped his fingers and did one of those miracle things and made me pregnant.
Joseph: God made you pregnant.
Mary: (Starts to sweat.) Yes.
Joseph: Mary, that is just so... completely...
(Mary's eyes squeeze shut.)
Joseph: ...COOL!
(Mary opens her eyes again, cautiously.)
Mary: You think so?
Joseph: Of course! Who wouldn't think so? Come on, we've got to tell everyone the news!
Mary: Maybe we should keep this between just the two of us -
Joseph: No, no, silly girl, this is way too important! Come on!
(Joseph grabs Mary's wrist and drags her out of the house. SCENE: The gathering square of Nazareth. A dozen well-dressed men, and the town's head rabbi, look on Joseph and Mary impatiently.)
Rabbi: What's this all about, Joseph? I trust there's a good reason for the fuss?
Joseph: Go ahead, Mary! Tell them what you told me.
Mary: Um... (She swallows.) God made me pregnant.
Rabbi, looking stern, yet understanding: Now, Joseph, you know you're not supposed to do that before -
Joseph: No, no, you don't get it! She's still a virgin! God made her pregnant directly!
(There's a long pause.)
Man #1: So, what you're saying here, basically, is that Mary tells you she's a virgin.
Joseph: Uh huh!
Man #2: And you haven't had sex with her.
Joseph: Uh huh!
Man #3: And now she's pregnant.
Joseph: Precisely!
Man #4: So you think that God did it.
Joseph: What other explanation could there be?
Rabbi: Joseph, that is just so... unbelievably...
(Mary holds her breath.)
Rabbi: NEAT!
(Mary exhales.)
Man #5: A miracle! A miracle right here in Nazareth!
Man #6: Wow! I thought that miracles only happened in Jerusalem!
Man #7: Come on! Let's spread the good news!
(They depart. SCENE: Mary is alone with her friend, Betty, in Betty's house.)
Betty: "God did it."
Mary: I panicked! It was all I could think of!
Betty: So who's the real -
(Mary lifts an eyebrow significantly. There's a brief pause.)
Betty: Ah. So that's why the rabbi went along with it.
Mary: Well, he thinks he's the father, anyway. Why, does it matter?
Betty: It puts some things in a different light.
Mary: Like what?
Betty: The rabbi has been telling all the pretty young girls that you, Mary, are the ultimate embodiment of feminine virtue, and when they grow up, they should be just like you -
Mary: I just feel so awful about the whole mess. What kind of thing is this to have hanging over my child's life?
Betty: You've got to put things in perspective, dearie. You told one little white lie. It's not as if you caused the fall of the Roman Empire.
Mary: But what if the Romans hear about it? I don't want my baby to end up being crucified!
Betty: No one's going to obsess about it that long. In a couple of months this whole thing will blow over.
Mary: I hope you're right...
(Exeunt Omnes.)