“All quotation is taken out of context”
This is almost a definition of a quotation as commonly used.
Enoch Powell himself was a victim of this as all public figures are. As a classical scholar his illusion to the ‘rivers of blood’ referred to the The Tiber of ancient Rome.
One is also reminded of the George Eliot novel where one of the characters remarks that the overuse of quotation from those far more literate and clever than oneself can kill conversation.
And so for all sorts of reasons we should be careful not to use quotation too frequently or as a substitute for thinking for ourselves. Anthony J Sargeant