Since my question was and since you answered as above, I must assume that disagreement over the deepest fundamentals of Christian belief is OK. Yes or no? Is it OK to find in Scripture that the Trinity is a false teaching? Is it OK to find that Jesus is not God?
Certainly not, again… sola Scriptura does not deny outside authorities such as creeds and confessions, however it makes Scripture the final authority. When one person, with no training, claims an ahistorical viewpoint or previously declared heretical viewpoint, it is not “ok” at all.
Within the different denominations of the Reformed tradition there exists confessions that dictate the normative beliefs within said denomination. (Specifically the WCF, LBCF, Three forms of unity, 39 articles, Book of Concord, etc.)
You’ll find, for example, that they all believe alike on the “deepest fundamentals of Christian belief”, as defined by the early creeds of Christendom. When someone denies some aspect said confession they may be placed under discipline until they recant or are asked to leave. (Sound familiar?)
But these confessions also go further in defining what that specific denomination believes. Generally these denominations will work together in evangelism and the like.
This of course requires these denoms to be faithful to their confessions and the word of God. There is, of course, in all of Christendom the problem of liberalism, post-modernism and other heretical notions that are by no means unique to Protestantism (surely you will acknowledge that.)
Is it OK to find that Jesus is really and substantially present in the Eucharist?
When one says “Jesus is really and substantially present in the Eucharist”, what do they mean? Where in Scripture is transubstantiation or the Lutheran view of in, with and under found? That Christ is “truly present” is apparent from Scripture, but to claim that the bread and wine turn into flesh in blood is not. There is no way that one can, from the grammar, context and content of Scripture define clearly the doctrine of “real presence” as Roman Catholics know it, however there is clear evidence from same means that Christ is God, the Spirit is God and that the Father is God and but they are one and yet three.
Therein lies the difference. Protestants are not “100% Tradition Free!”, no matter what some might suggest, rather, they rest final authority for all matters of faith and salvation on the Word of God alone.
Finally, as a counter question: Is it “ok” to believe that God knows the future intimately, or just that he has knowledge of all possibilities? If either view is “ok” within the Roman Catholic church, why does the same church deny the right for other aspects of the faith? Is this an example of a “secondary issue” that Rome allows private interpretation on?