Let me cut to the chase here. It is impossible to found a society based on the idea of "liberty" or "fairness" or "justice" or whatever because everyone disagrees about what these ideas entail. Your version of "liberty" is going to be much more preferential to your position than my definition of "liberty". And everyone is going to have to have their own version of "liberty" or "fairness" or whatever.
So, guess what. In a society such as this someone is going to have to decide which version of "liberty" or "fairness" or "justice" is going to prevail. And because you can't appeal to God for authority, well then you have to appeal to force. If I refuse to go along with a version of "liberty" that I personally disagree with, then you're going to have to "initiate force" against me to comply, in direct contravention of your stated "gold standard" for libertarianism.
And who gets to decide what "liberty" or "justice" or whatever actually means? An intellectual elite? The people with the most guns? Who?
From my point of view, libertarianism--the atheistic variety--looks like this: an abstract idea that requires some sort of elite to make arbitrary decisions to stop that abstract idea from plunging into absurdity. These arbitrary decisions are backed up with force.
Gee, sounds like tyranny to me.
Sorry for your confusion. There is no arbitrary decision making elite required. Initiating force is wrong. That's the deal.
Just correcting a few omissions
So we should base our society on God because we all agree there?
And because you can't appeal to God for authority, well then you have to appeal to force.
Explain, please how we appeal to God's authority. Who is to be the intermediary? How do we establish they're not just making stuff up?