“Using one’s conscience” without the Properly Formed qualification is Protestant and relative.
Which is essentially a meaning-less statement since the term "Protestant" as typically used by Catholics is so broad as to be meaningless in this context, since it includes everything from the ultraconservative scholastical Puritans - who definitely believed in a Scripture- formed conscience as opposed to doing what seems right otherwise - to Unitarianism with its rejection of any supreme standard on Truth.
Rather than the easy believism Catholics (with a church half full of liberal members) associates with sola fide, in Puritan Protestantism there was often a tendency to make the way to the cross too narrow, perhaps in reaction against the Antinomian controversy, as described in an account (http://www.the-highway.com/Early_American_Bauckham.html) of Puritans during the early American period:
“They had, like most preachers of the Gospel, a certain difficulty in determining what we might call the ‘conversion level’, the level of difficulty above which the preacher may be said to be erecting barriers to the Gospel and below which he may be said to be encouraging men to enter too easily into a mere delusion of salvation. Contemporary critics, however, agree that the New England pastors set the level high. Nathaniel Ward, who was step-son to Richard Rogers and a distinguished Puritan preacher himself, is recorded as responding to Thomas Hooker’s sermons on preparation for receiving Christ in conversion with, ‘Mr. Hooker, you make as good Christians before men are in Christ as ever they are after’, and wishing, ‘Would I were but as good a Christian now as you make men while they are preparing for Christ.’”
And reverence of God and His word by the Spirit with more than a basic concurrence on core beliefs enabled this testimony by a noted Catholic, the famous French Catholic political thinker and historian, Alexis de Tocqueville (1805-1859):
The sects that exist in the United States are innumerable. They all differ in respect to the worship which is due to the Creator; but they all agree in respect to the duties which are due from man to man. Each sect adores the Deity in its own peculiar manner, but all sects preach the same moral law in the name of God...Moreover, all the sects of the United States are comprised within the great unity of Christianity, and Christian morality is everywhere the same...
n the United States the sovereign authority is religious, and consequently hypocrisy must be common; but there is no country in the whole world in which the Christian religion retains a greater influence over the souls of men than in America, and there can be no greater proof of its utility, and of its conformity to human nature, than that its influence is most powerfully felt over the most enlightened and free nation of the earth...
The Americans combine the notions of Christianity and of liberty so intimately in their minds, that it is impossible to make them conceive the one without the other; and with them this conviction does not spring from that barren traditionary faith which seems to vegetate in the soul rather than to live... Thus religious zeal is perpetually warmed in the United States by the fires of patriotism. These men do not act exclusively from a consideration of a future life; eternity is only one motive of their devotion to the cause. If you converse with these missionaries of Christian civilization, you will be surprised to hear them speak so often of the goods of this world, and to meet a politician where you expected to find a priest. (Democracy in America, [New York: A. S. Barnes & Co., 1851), pp. 331, 332, 335, 336-7, 337; http://xroads.virginia.edu/~HYPER/DETOC/religion/ch1_17.htm)
And Benjamin Franklin also advertised,
And the Divine Being seems to have manifested His approbation of the mutual forbearance and kindness by which the different sects treat each other, and by the remarkable prosperity with which He has been please to favor the whole country. (Benjamin Franklin, "Information to those who would Remove to America" In Franklin, Benjamin. The Bagatelles from Passy. Ed. Lopez, Claude A. New York: Eakins Press. 1967; http://mith.umd.edu//eada/html/display.php?docs=franklin_bagatelle4.xml. Also, John Gould Curtis, American history told by contemporaries .... Volume 3, p. 26)
Golly!
What might that BE??