No, murder would be wrong even if it wasn't popular belief, because it violates the rights of the person being murdered (i.e. the right to live). It is also popular belief that claiming "Christ is not the Son of God" is wrong, however, people have a right to free speech, and that free speech does not infringe upon the rights of anyone else.
Where does "right to live" come from? Who gives us that right? Well, if your an atheist, then that would be nobody/being. Then you can only assume that you have that right. But in that instance saying right to live, would be no different than my right to kill you. Your rights are based on what you believe and mine are based on what I feel to be my rights. Whose right is greater? How do you measure that? If I kill you, doesn't that mean you've lost all right to live? Isn't abortion taking away ones "right to live", yet that's legal.
If you believe that these beliefs come from no higher being, then you can only believe they come from yourself. And therefore, nobodies rights can be greater than anothers.
In this instance how would you retain order in the world? Only through popular belief/vote, or through dictates of the government. Whatever most people believe is right, or the government dictates to be right, will be considered right. Your free speech example is the perfect defense for this! In Communist countries they aren't afforded the "right" to free speech. That must mean our rights, and their rights are different. How is this possible if we're all human beings? If free speech were an actual "right", could a government power take it away? No. So, one must have to accept that we are GIVEN rights, not born with them.
Given the right to live.
Given the right to free-speech.
Given the right to bear arms.. etc. etc.
And in relation to the subject at hand....
Marriage isn't a right unless government gives it to us, just as free speech isn't a right unless it gives it as well.
Well, our government is a republic, which practises democracy on occasion, and one of those democratic votes was whether marriage should be for man-and-woman? Well, popular vote (in the states that held it) decided that marriage
would be for opposite sexes.
Now, will this remain? I doubt it. Because it's popular vote, it can always change. Theoretically killing could become ok, if popular opinion were to say it should be. That in itself proves that without any higher force, "morality" is only what the greater population wants it to be.
Now, if you believe there is a higher power (God, Allah, Brahman, Vishnu....), then you could bring the argument of morality to an entirely different degree. Unfortunately I don't have time to do this, and it's relatively unimportant considering the topic, and the forum its in. I'm sure you know the better part of it anyways.
I realise that a lot of that could probably use a lot of clarification, but I've gotta get to a professors office during his hours, so I have to leave shortly. Also, if I left out entire sentences (which I often do when I don't proofread...) then some things probably weren't articulated well, and you'll have to pardon me.
One more thing...... This message was directed mostly towards Spinkles. I find that when I direct an arguement towards one person, then many times somebody else jumps in and starts taking things completely out of context because they don't know what we're actually talking about. I'm getting tired of defending my statements against people who, either by lack of knowledge of the discourse, or by lack of understanding, decide to put in their "2 cents". I know I'm not the only one this happens to, and forgive me if I do it to you.
With that being said, if you aren't capable of deep thought, or thinking out of the box, then you should stay away from a philosophical debate like this. Not to sound arrogant, or to make others sound stupid, but if we want to intellectually argue these points, then you have to know what's being said, and dig a little deeper than what high school taught you.
Hopefully I'll have time to edit this later in the day, but I have to jet for now.