Bibliography began to fall behind the times when ISBN's appeared. Even today, most editors will insist that a book be cited by publisher and location. The way publishers merge and split, a book can be handled by three different publishers before hitting print (a textbook I co-authored was). A publisher may have offices in half a dozen cities, and the actual printing is done someplace else far away. Yet the long obsolete practice continues, while the ISBN, a unique identifier, still isn't the standard. There are now analogues for journals and musical scores.
Nowadays, if you doubt the veracity of a statement, you can paste it into Google and get hits all you like. And if you want a stricter filter, Google Scholar. Citing references is still a useful way to direct readers to especially useful sources. Or obscure ones, like, the last American to die in combat in World War II was killed on Guam by Japanese holdouts after Japan had surrendered (http://auntiecharo.guam.net/archives/2005/08/index.html). But there simply is no longer any need to cite sources for things like the overall history of World War II or who signed the Declaration of Independence or what happened in the Battle of Gettysburg. Actually, for things that fall into the domain of common knowledge, there never was.
So let's be brutally blunt. The people I see on line demanding sources don't give a rat's @$$ about rigor or intellectual standards. In fact, even when you do provide sources, people will simply ignore them. For example, the whole "Giordano Bruno was a martyr to science" myth has been decisively demolished (See the, ahem, references). So when I've actually cited these sources, people go right on parroting the Bruno myth. So people who ask for references on line don't really care about the references.
It's solely a cheap and lazy way to pretend to be scholarly. Ditto Wikipedia bashing. Quite a few tests have compared Wikipedia to conventional print encyclopedias, with Wikipedia coming out looking very good. However, Wikipedia is not aging gracefully. Its bureaucracy is ossified and commonly abusive, and articles with any controversial content can be (and increasingly are) shouted down. One of the most egregious cases was that of historian Timothy Messer-Kruse, who found that the truth about the notorious Haymarket Affair of 1886 was a good deal more complex than the conventional simple victimization narrative implied. His attempts to edit the Wikipedia entry were shot down, his attempts to use the actual trial transcripts as sources rebuffed, and even after publishing two scholarly books on the subject, his views are treated as footnotes (see the, er, references). In fact, his article on the affair in The Chronicle of Higher Education quotes Wikipedia editors as saying, in effect, they consider only secondary sources (the exact opposite of scholarly practice) and do not attempt to evaluate sources critically at all.
To consider another example, the article on "the Rapture" originally focused heavily on the teachings of 19th century Scottish preacher John Nelson Darby, who seems to have been the person most responsible for popularizing the doctrine. The idea that the Rapture is a modern cult doctrine didn't sit well with modern believers, and today the article is cluttered with references to earlier Rapture-like teachings, whether they had any lasting impact or not, and Darby's seminal role is thoroughly obscured, though his biographical article is (temporarily at least) clearer.
Like most innovative academic enterprises after a short time, Wikipedia has fallen into the hands of the fuddy-duddies. The problem with academic publishing is that overly tight quality control stifles innovation but wide-open publishing, like many of the open-access on-line journals, releases raw sewage into the marketplace of ideas. I used to ask how bad it could be if we just let anyone publish their ideas. Now I know: real bad. However, none of those problems lessen the utility of Wikipedia as a source of basic facts and, still more, a source of references. And if you have any doubt about some fact in Wikipedia, cut and paste it into Google (or Google Scholar). Most of the people who dismiss Wikipedia as a source wouldn't have a clue where to find a scholarly reference and couldn't read one if they had one.
No, neither Wikipedia nor print encyclopedias are legitimate scholarly sources. So why does every university still have print encyclopedias? Because they're useful places to go to get an overview of a topic, as well as find references (Wikipedia's article on Galileo cites 181 sources). By the way, another reference on Galileo et al is "Galileo Goes to Jail and Other Myths about Science and Religion," edited by Ronald L. Numbers, Harvard University Press, (2009) ISBN's 0674054393 and 9780674054394. Presumably Harvard University Press is acceptable?
B-but Burden of Proof
I had someone hotly disagree with these ideas recently, falling back on the idea that the person who makes a positive claim has the burden of proof.
So that means if a creationist disagrees with me saying evolution is a fact, I have to provide him with references showing otherwise? Some sovereign citizen type takes issue with my saying the laws apply to him? A modern-day geocentrist (yes, that's a thing) demanding proof that the earth goes around the sun?
Nope. Those particular examples are all tendentious. The person demanding "proof" has no intention of accepting anything you offer him. He just wants an argument. And that applies to at least three fourths of the cases where someone on line demands references. When I criticized Neil deGrasse Tyson's remake of Cosmos for its historically inaccurate glorification of Giordano Bruno, I got plenty of people demanding references. It so happened I knew of several (cited below). Did anyone say "Oh, I guess I was wrong?" (Left as an exercise to the reader).
In many other cases, people ask for references because they just don't know. That's fair and reasonable, but, if the references are well known to anyone well versed in the subject matter, the person has just revealed himself to be unqualified to engage in the debate. Courtesy might move me to provide references, but don't try to pretend you're informed. You're not. There's a vast gulf between "I don't think you can back up your claims" and "I don't know enough to evaluate your claims." So if you demand to know how scientists can be so sure rocks are hundreds of millions of years old, I can point you to a couple of good books. But don't pretend you're qualified to argue with scientists about the age of the earth. You have just revealed you don't have a clue about the facts. In political debates, if you're going to challenge the opposition, you're not informed if you don't know what they commonly use for sources.
Once someone has provided references, they have met the burden of proof. Now the burden is on you either to agree or provide counter-evidence. And "Breitbart isn't a valid source" doesn't cut it. Breitbart might not be a reliable source, but the only permissible argument is "Breitbart is wrong about this particular issue, for these specific reasons."
ReferencesGalileo and the Specter of Bruno, 1986; Lerner, Lawrence S. and Gosselin, Edward A., Scientific American, Vol. 255, Issue 5, p.126.
Was Giordano Bruno a Scientist?: A Scientist's View. Available from: https://www.researchgate.net/publication/253432071_Was_Giordano_Bruno_a_Scientist_A_Scientist%27s_View [accessed Jan 6, 2016], Originally published in American Journal of Physics, 1973, v. 41, no. 1 p. 24-38.
Messer-Kruse, Timothy. "The “Undue Weight” of Truth on Wikipedia." The Chronicle of Higher Education (2012). http://chronicle.com/article/The-Undue-Weight-of-Truth-on/130704/ [accessed 3 July 2016]
Wikipedia Policies Limit Editing Haymarket Bombing:
http://www.npr.org/2012/10/03/162203092/wikipedia-politicizes-landmark-historical-event [accessed 3 July 2016]