The point is that if ones culture says sleeping around is alright, then one does not need some other culture to tell you that such is wrong. If you buy such, then I suppose we don't really disagree.
If what you mean is simply that just because your culture tells you that sleeping around is all right doesn't make it so, then of course I agree. Sleeping around is wrong regardless of what anyone says. However, if you mean that reason alone could tell you this if you'd been brought up to think otherwise and had never been exposed to other views, that's much harder to maintain. My Thomistic side would like to agree with you, but I can't see how it would work practically.
But even before God did such, we still knew and were responsible to know various things due to General Revelation.
General revelation is only possible because of God decreeing incarnation. There can be no true communication between God and man unless God becomes man. The whole book of Hebrews makes this point, showing how even the Old Testament makes sense only because it points to Jesus.
That we function in community is cool and true, but at the end of the day, "My culture didn't teach me that", is not a valid excuse.
No, you're still condemned before God. What does that have to do with my point about how we acquire epistemic skills?
I would say that right reason makes belief in the Christian God inevitable.
Ah, but how do you learn how to reason rightly? Who teaches you? We're back to pre-modern theories of pedagogy, such as I am advocating.
And I am supporting something along the lines of enlightment-style rationalism. I think such folks were not critical enough in their use of reason, and that is the reason, it was not as effective as they had hoped.
I'd say it was way too effective: they went insane. You want some real rationalists using reason rigorously? Go read Bertrand Russell, or A.J. Ayer and the logical positivists. You want to see where "objectivity" gets you? Read those guys. Myself, I'll stick with C.S. Lewis, Michael Polanyi, and others who advocate a return to a pre-modern model.