I came across this nugget after a number of hours trying to track down a context to a Luther quote:
The venerable champions of Protestantism, the Rev. Joseph Mendham and the Rev. George Stanley Faber, repeatedly warn their readers to accept with the greatest reserve and caution any statement, theological or otherwise, of a startling nature from the pen of a Romanist, and to reject it until verified by a careful examination of the originals. But, as their testimony may be deemed partial, I will add the remarkable testimony given in the Translator's preface of Dr. Dollinger's "Fables respecting the Popes of the Middle Ages," a translation undertaken with the sanction of the author,—himself a Romanist. The charge of literary fraud indulged in by Roman Catholic writers is thus delicately expressed :—
"It is impossible to live long among those who are devoted to the interests of the Vatican, or to read much of the literature that is written in support of those interests, without feeling that the conception of truth entertained by those advocates is a saddening travesty of the sacred reality. In some cases the sense of truth, the love of truth for its own sake,— nay, even the very power of discriminating between truth and falsehood,—seems almost lost"!
source and primary source
By the way, the quote I was looking for turned out to be spurious. Of course, not every person in communion with Rome quotes sources poorly. However, in my Luther studies, more often than not, truth is slain in the street.