I have only found "Ignorance is bliss", is there any other?
Not knowledge per se, but the classic warning against the pursuit of knowledge is curiosity killed the cat:
“Curiosity killed the cat” is a proverb used to warn of the dangers of unnecessary investigation or experimentation. …
Inquisitiveness can lead one into dangerous situations.
Prov. Being curious can get you into trouble. (Often used to warn someone against prying into other’s affairs.)
- Jill: Where did you get all that money?
Jane: Curiosity killed the cat.
said to warn someone not to ask too many questions about something
I could tell you, but then I would have to kill you.
I could tell you, but then I’d have to kill you has become a way to let someone know they’re asking you something you don’t want to answer (and a rather colorful way of telling them to mind their own business!).
This line comes from "The Hounds of Baskervilles" featuring Sherlock Holmes. Here is the exchange:
Sherlock: I never did ask, Dr. Franklyn. What is it exactly that you do here?
Doctor: Oh, Mr. Holmes, I would love to tell you, but then, of course, I’d have to kill you.
Sherlock: That would be tremendously ambitious of you.
The line has since appeared in many movies, including Top Gun with Tom Cruise. Here’s a handy YouTube video compiling many snippets with this line and variations on it.
a phrase said in answer to a question that one does not want to answer. Don’t ask.
Often heard in settings related to espionage and high security levels, the phrase “I’d tell you, but then I’d have to kill you” is itself probably a Dead Horse Trope by this point – whether for a serious straight use or not.
As the quotes above indicate, this has become something of a joke.
While not exactly an idiom or proverb, the phrase knew too much is evocative of the films The Man Who Knew Too Much, in which a man is murdered for learning of a criminal conspiracy. References: [IMDb 1934], [IMDb 1956], [Wikipedia 1934], [Wikipedia 1956].
There’s a well-known proverb, “A little learning is a dangerous thing,” often misquoted as “A little knowledge is a dangerous thing.” For years I (mis)understood this to mean that knowledge is dangerous — so dangerous, so potent, that it is dangerous even in small quantities. But when one sees the complete sentence, which appears in Part 2 of An Essay on Criticism by Alexander Pope:
A little learning is a dang’rous thing;
Drink deep, or taste not the Pierian spring:
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.
it becomes clear that the message is that partial or incomplete knowledge is dangerous, while thorough or complete knowledge is a good thing.
A small amount of knowledge can mislead people into thinking that they are more expert than they really are.
Knowing a little about something tempts one to overestimate one’s abilities.
and from this we get the phrase (again, not exactly an idiom or proverb) knowing just enough to be dangerous.
"For in much wisdom is much grief: and he that increaseth knowledge increaseth sorrow" Ecclesiastes 1:18
…is another example, beloved of my dear late mother, and is almost identical in meaning to “ignorance is bliss”.
The linked source adds “over”, which is a variant. I dislike the latter as I feel it spoils the rhythm and near-rhyme of the final words; but that may just be familiarity with the former version.
This one is more for personal knowledge (like your partner is cheating on you) than for book knowledge, but it definitely discourages knowledge:
What you don't know can't hurt you
One saying that has some application to the idea of avoiding the acquisition or dissemination of knowledge is:
"He who is deaf, blind, and silent will live a hundred years in peace"
According to various sources this is a translation of a traditional Sicilian proverb,
Cu è surdu, orbu e taci, campa cent'anni 'mpaci
I cannot vouch for whether the original source is correct but the English translation does have some small traction.
EDIT: There is a striking parallel with the English saying, "see no evil, hear no evil, speak no evil", which, as pointed out in a comment below, is associated with the "three wise monkeys" commonly depicted in statuettes and comprising a cultural phenomenon that has spread from Japan since the 17th century. It is not clear to me what direct connection, if any, exists between the Sicilian phrase and the proverb associated with the three monkeys.
I'd rather entrust the government of the United States to the first 400 people listed in the Boston telephone directory than to the faculty of Harvard University.
William F. Buckley, Jr., according to this source.
You'd have to have a Ph D from Harvard to believe something that foolish.
No attribution that I could find
The Story of Adam and Eve
Nobody has yet mentioned the story of Adam and Eve. Eve eats from the Tree of Knowledge and dooms humanity to original sin.
"[...] but from the tree of the knowledge of good and evil you shall not eat, for in the day that you eat from it you will surely die."
Then the eyes of both of them were opened, and they knew that they were naked; and they sewed fig leaves together and made themselves loin coverings.
"Knowledge is Power"
At first, it might not seem like a proverb or idiom that discourages knowledge but think about it from the perspective of a large corporation or a large (and possibly) government. Suppressing knowledge diminishes the power the citizens (employees) have thereby augmenting their own power.
So to those governments or corporations or entities, it warns (and reminds) them of the dangers of encouraging knowledge.
A 19th-century proverb from the Indian subcontinent:
Educating your girl is like watering another man's field.
(Several variations can be found online)
Meaning and context
This came to be when the male-dominated society was heavily biased against women empowerment. The point of this statement is that the education of girls is as unbeneficial and optional as watering another man's fields. Your girls aren't actually yours; they all have to go to another man's (father-in-law's and husband's) house at the end. If you educate your girl, all you're doing is enlightening someone, who is to be another man's property.
Among the Muslims, it was even more popular. Earlier, Muslims practiced the Purdah and no Muslim girl was allowed see or talk to any man (or woman for that matter), except her own mother and father (and after they're married off, their in-laws and husband). They were taught only to read Arbi and Farsi. They were not literate even in their own tongue. Hindu women, on the other hand, were educated to some extent, if not as much as their male counterparts.
that it's not general and applies to only women. And it's more of a prejudice than a proverb. In addition, only people who understand the Indian culture will understand this. (By India, I mean the whole Indian subcontinent.) Don't think that such beliefs still persist. Indian people have a much more improved mindset now, and most women are educated and seek empowerment.
A few idiomatic near misses - 'too clever by half' and 'too smart for their own good' - usually meaning you're acting as if you have more knowledge than you really do, or applying too much complexity to a problem, but also can be used to mean someone who really does have more knowledge than they need.
The thinking classes: too clever by half
A study attacks today's intellectuals for being too willing to dumb down. Rubbish, it's just a new style of democracy https://www.theguardian.com/books/2004/sep/12/society
Too clever by half
A third of graduates believe they are overqualified for the job they are in, according to research from Kent University.
Also 'knows too much', though that's more often operational knowledge rather than learning.
Against the backdrop of the Cold War, in 1955, Albert Einstein and Bertrand Russell issued a famous joint statement which is often summarised by an extract:
It's known as the Russell-Einstein Manifesto.
Also related is this quote from Cicero:
The idea seems to be that "higher" learning sometimes enables one to believe things which normal minds cannot ... And this is at least not always a good thing.
From William Shakespeare's Henry VI, Part2, Act IV, Scene 2: "The first thing we do, let's kill all the lawyers" said by Dick the Butcher, who was a follower of the rebel Jack Cade. Cade thought that if he got rid of the people who understood the laws and disrupted order, he could become king. Rather than being an insult or lawyer joke, Shakespeare intended this as a compliment to attorneys and judges who instill justice in society. Clearly, the flip side is that if you have too much knowledge (admittedly of a specific type in this instance), you can be a target.
Consider also Mao Zedong's killing of teachers during the Cultural Revolution: "The early enforcers were the Red Guards, a proxy army of children and young adults that violently struck out at anyone not toeing the Maoist line. Intellectuals, educators as well as artifacts were all targeted. A favorite method was to whip their elders with the heavy metal buckles on their leather belts." (http://www.cnn.com/2014/06/04/world/asia/china-maoist-scars/index.html)
Akin to Shakespeare on this point, one Maoist slogan is "The three supremes (三个至上) 2007" "It might sound like a Motown group, but in Hu Jintao's mind it was a way of controlling an increasingly reform-minded judiciary. 'In their work, the grand judges and grand procurators shall always regard as supreme the party's cause, the people's interest, and the constitution and law,' he said. Mr Hu effectively shut down the discussion of legal reforms by appointing as Supreme Court president Wang Shengjun, an apparatchik with no legal training. Mr Wang set about making sure the courts obeyed the three supremes doctrine. Since then, the interests of the party have reigned supreme over the other two supremes. (http://www.bbc.com/news/world-asia-china-24923993)