I think we can definately agree on this, that more knowledge would be helpful going both ways. It's not that I can't see the kernel of truth in Newman's statement, I just think it's an overstatement. Maybe what bugs me about it is that I think Catholic and Orthodox apologetics are overstated to begin with, so to use flourishes like that is even more than a bit much. Let me play the part of a Protestant here for a moment. Let's take the Biblical canon, which many Catholics and Orthodox use as an argument for the authority of the Church. Thus you often hear the line in debates, at least in chat rooms, "Where did your Bible come from?" with the point of course being that the Catholic/Orthodox Church gave it to them. "And why then did the Protestants take books out?" But if I was a Protestant, I wouldn't see this being "deep in history," I'd see it being deep in apologetics.
The Church settled the Scripture? Athanasius? Carthage? Rome under Pope Damasus? Then why did Jerome, the most famed Bible scholar, reject the deuterocanonicals from his canon after these councils (he was even the personal secretary of the pope for a while)? Why did Pope Innocent exclude Hebrews from his canon in a letter written in 402? Why did Junilius talk of the deuterocanonical books being disputed in the 6th century? Why did John of Damascus accept none of the deuterocanonicals, but add the Canons of the Holy Apostles (attributed by him to Clement) in his NT canon? No, if I was a Protestant I certainly wouldn't buy into the claim that the Bible was settled in the 4th century. If anything, the canon issue is evidence against Church authority, because it shows how even when it comes to the most important source of information, there were disagreements for a very long time. Not on all of the books, admittedly just on less than a dozen, but if the Church really was all that the apologists claimed that it was, then it could have been settled.
Now, I didn't mean to go on a rant, I'm just saying that if I was a Protestant "deep in history," those would be some of my thoughts. So if I had someone come in then and say "To be deep in history..." to me, I would probably not react very well. And then the "30,000 denominations" thing gets thrown in. As I understand it, the people who put out numbers that large count basically everyone and their brother as a seperate Church. That means that Catholicism counts for hundreds, and so do the Orthodox. We don't need to get into the details, everyone knows that Orthodoxy and Catholicism each have lots of groups who are (to put it nicely) not currently in communion with the overwhelming majority of Orthodox/Catholics. And then there are some even further out, like vagantes, who nonetheless might technically, in some vague fashion, have apostolic succession or something resembling it. Besides, (again, if I was a Protestant...) who are the Catholics or Orthodox to talk about divisions, when they've been divided from millions of Christians (e.g., non-chalcedonian copts) for 1,500+ years?
One could argue that the main reasons that so many Protestant groups have survived and multiplied is because of better communication and religious freedom. There were hundreds of break off groups even in the 2nd and 3rd century, thus making it necessary for people like Ireneaus and Hippolytus to write long works refuting heresies. Even the Scriptural writers like Paul and John dealt with break offs and heretics in the first century. I do not say this to excuse Protestant fracturing, of course. It is sad even for me when Christians divide, and I am glad when there is some healing (e.g., ROCOR and the MP). But things are rarely as simple as people would like them to be. Or even as simple as they read about in history books. I suppose some of what I am trying to say here (and I feel that I'm doing poorly) was put like this by Descarte:
...and even the most faithful histories, if they do not wholly misrepresent matters, or exaggerate their importance to render the account of them more worthy of perusal, omit, at least, almost always the meanest and least striking of the attendant circumstances; hence it happens that the remainder does not represent the truth, and that such as regulate their conduct by examples drawn from this source, are apt to fall into the extravagances of the knight-errants of romance, and to entertain projects that exceed their powers.
I found that the deeper in history I went, the mirkier the waters were. I'm not suggesting that everyone should end up in a see of agnosticism... I am just very wary I guess.