Turretin affirms tabula rasa with some qualifications, which are, to paraphrase, that while humans are not born with declarative knowledge, they are born with innate logical principles that may be worked out. Which is pretty much identical to the epistemology of Noam Chomsky. Also Thomas Aquinas. All that to say, I think you should reconsider. Whatever conclusions we come to regarding epistemology, they need to lead to a strong affirmation of objective "facts", or we won't be able to conclude our heathen neighbors under sin. We should not be existentialists.
I am familiar with Turretin here. He says, as you summarize:
It is certain that no actual knowledge is born with us and that, in this respect, man is like a smooth tablet (tabulae rasae). Rather the question is whether such can be granted at least with regard to principle and potency; or whether such a natural faculty implanted in man may be granted as will put forth its strength of its own accord, and spontaneously in all adults endowed with reason, which embraces not only the capability of understanding, but also the natural first principles of knowledge from which conclusions both theoretical and practical are deduced (which we maintain).
—Francis Turretin, Institutes of Elenctic Theology: First through Tenth Topics, ed. James T. Dennison, trans. George Musgrave Giger, vol. 1, 3 vols. (Phillipsburg, NJ: Presbyterian and Reformed Publishing, 1992), 6; italics original; bold and underline added.
I don't think anything I said disagrees with Turretin. I never said there are no
objective facts. I said there are no
brute facts, which Frame defines as “facts apart from any interpretation" (John M. Frame,
A History of Western Philosophy and Theology [Phillipsburg, NJ: Presbyterian and Reformed Publishing, 2015], 743). Objectivity and interpretation are two different areas of concern, although certainly related. All facts are objective, but they are objective
because they exist in the mind of and are interpreted by the God who created them. So in order for human beings to come to
objective knowledge about anything, presupposing the truth of God is necessary (Prov. 1:7). This doesn't leave any room, for the unbeliever to be excused of their sin, though. They all know the truth about God, but they suppress it (Rom. 1:8). They have access to all the same
objective facts that you and I do, but they pretend that they are
brute, existing in and of themselves (Rom. 1:21-22). But all facts, as they stand, are facts because they are created and preinterpreted by God.
That's all I meant. But I disgress. This thread isn't about epistemology, and my inner Van Til could wax eloquent here, so I'll stop here.