It is a quote from George Orwell, usually given as: "Gentlemen sleep peacefully in their beds each night because rough men stand ready to do violence on their behalf."
It is not from one of his books, he used to lecture on liberty and I think that is its source. Some people have a great tendency to denigrate Law Enforcement and the Military until they are needed. Orwell was reminding us that we need them at all times.
Thanks OldRoger.... I already found the quote useful in discussion with a liberal friend. He was questioning the legality and ethics of the CIA killing known terrorists without a trial. He did not have a good comeback. I think it made him think.... which we all know is a big step in the right direction for a liberal.