"You can just as well act some other way in the next instant -- as the quote says.
Of course, you have to define civilized before it makes any sense to discuss acting civilized or uncivilized, there are civilizations that are barbaric and those that are pacifist. Pirates have a civilization, and may have a code, and consider themselves civilized -- and who are we to argue, if there is no moral authority outside what we imagine, make up, and act out of our own initiative?"
Conjuring morality out of thin air is a good trick. Like any animal, when I itch, I scratch. When you itch, I may sympathize, or I may be amused at your discomfiture. That choice is mine.
Similarly, I can choose many paths as you have suggested. What motivates me to choose a "right" path?
It is my nature to go quietly about the world, making little noise in the forest. I wish to see before I am seen. This seems practical, in all walks of life.
If we meet, I will keep a watchful and wary eye on you. If you don't like that, hide, but hide well. I will be watching for that as well.
It is not my nature to seek confrontation, or advantage in it. I seek to earn my way, and have a proper title to things I earn or trade for. I am aware that others think otherly. Accordingly, I will also watch my possessions.
Thus, being Civilized, in my definition, means being able to reliably enter into contracts and fulfill them. That's about it. If you can't or won't keep your word, you aren't civilized.
A civilization or a society may be barbaric, but if they will give their word and keep it, then they are civilized enough for me.
In regard to "moral authority", that is a conceit of our age. I have no authority over your behavior any more than you have over mine. If you will not honor contracts and keep your word, we will not do business. We may have transactions, but they will not be ordinary business.
What is the "right" path?
I seek to earn my way, and have a proper title to things I earn or trade for.
Why?
When I'm driving, I move over when a faster car is behind me, because I wish others would do the same for me. In some sense it is selfish, because I do it to gain. In another sense it is stupid because the chances that the person behind me will remember this and do the same later for me is miniscule.
Once in a great while, when I am in a particular rush, I change my driving style, into something akin to what I normally criticize. I do so because I gain from this change.
I don't go 100 mph, even though I certainly could do so safely, because there is a law against it and I could get caught and get a big ticket or get thrown in jail, but I and many others go whatever speed we think we can get away with.
Man's nature is to do what is best for us, to cooperate only so long as it is convenient and helpful to us (Star Trek illustrated this using Romulans to speak this truth). Civilizations have existed on this principle alone, with the wealthy oppressing the rest of humanity because they only had to cooperate with others who had power, so they could treat most people like dirt. We did so in this country for 100 years of slavery because we could do so.
Thus, being Civilized, in my definition, means being able to reliably enter into contracts and fulfill them.
Which works fine if you associate with a group of people who agree with your definition of civilized; and will be useless if you hang out with a group of people who believe being "civilized" means reneging on contracts when it suits them, and valuing only the ability of others to inflict pain to protect their interests. These people would respect power over honor, and that would be their "civilized" nature.
You can of course associate with others who hold the same beliefs as you about civilized living; but then you have organized about a set of common beliefs -- beliefs being things you hold true with no proof of them being so.
In regard to "moral authority", that is a conceit of our age. I have no authority over your behavior any more than you have over mine.
I've got a police force with guns that says differently. I elect people who pass laws which are enforced by these police officers, and if your behavior does not comport with what I through my representatives thinks it should, my authority through those means will be made clear to you at the point of a weapon if necessary.
Of course, this is the morality of the majority, and can be tyranny excecpt if, as our founders noted, that majority has itself been bound by a higher, more constant morality.