Two arguments are frequently made which I think have no merit.
1) "It interferes with readability of the articles." Sure it does,
but that's a technical issue, and _if we wanted solutions_ we could
deal with it through tehnical means. We could define better visual
apparatus for references. One of the examples I keep pointing to is
Laura Hillenbrand's book, "Seabiscuit: An American Legend," not
because it's the only book that uses this style but because it is an
extremely readable bestseller. It is densely cited, but there is not
a single mark within the text. Instead, the references are placed at
the end. They are indicated by chapter, page number, _and phrase_.
This would require modifications to work with Wikipedia, but that can
be discussed.
Wikipedia has a unique _requirement_ for very dense references,
_denser_ than those found in research papers or nonfiction books, so
it is not surprising that traditional solutions are not perfect for
Wikipedia, and that we will need to think of better approaches.
2) "If it appears in numerous textbooks it does not need a citation."
This is silly. The problem is that there is no way the reader or
anybody else can tell the difference between a sentence which lacks a
reference _because somebody has checked_ to make sure that it appears
in numerous textbooks, and a sentence which lacks a reference
because_ someone just typed it in off the top of their head_. They
look the same.
Even if someone goes over an article with a fine-toothed comb today
and has made sure that none of the unreferenced material needs
references, without any sort of markup apparatus there's no way
anyone can tell a week later which portions of the text have been
reviewed.
In other words, if we don't drop something into the article to leave
a breadcrumb trail to where the fact was found, then any work we do
in fact-checking will be wasted effort because it will be obsolete a
week later. We need some kind of marker to where the fact was found.
And the marker needs to be readily visible... at least to those
interested in seeing it... so that anyone can see how carefully the
article has been fact-checked and _which facts in it_ have been checked.
Finally, which is easier to do: check to make sure that a fact is
contained in _three_ textbooks and say "good, it doesn't need a
reference" and not put one in? or check to make sure it's in ''one''
textbook and cite the source?
I sometimes think that at least some people who object to citations
do so because what they really want is to _establish themselves as
authorities_ through social interaction with other page editors. That
is, they want their Wikipedian colleagues to recognize _them_ as
reliable sources, and agree that any fact inserted by
[[User:Pantomath]] does not need a citation because everyone agrees
that User:Pantomath knows everything.