No, There's No Secret Conspiracy To Hide The Talmud from Non-Jews.
The Quote
“If a Jew should wish to explain some of the Rabbinic literature, he must only provide a false explanation. One who transgresses this commandment will be put to death. Providing information about our attitude toward the gentile religion would be equivalent to killing all the Jews, for if the gentiles would know what we teach about them, they would kill us.”
Libbre David 37
The Reality
This quote – and indeed the entire book – are made up out of whole cloth.
There is no book called “Libbre David.” It just does not exist. “Libbre” is not even a word in Hebrew — it most likely has Latin origins and is meant to be “Books of David.” However, no such book exists. The only place one finds it is in lists of fake “Talmud quotes” on the Internet.
To verify this, one simply needs to find any list of books of the Talmud. You could find it on Wikipedia or any of numerous other sites. In no case will you find a book called “Libbre David” (or anything similar).
https://hebrewbooks.org/pdfpager.aspx?req=20431&st=&pgnum=40
Summary:
It is a complete and utter fake. The quote (and book) do not exist.
