[Eric in the Ozarks]

Count me as someone who didn’t know until recently that “An armed society is a polite society,” was Heinlein’s quote...

[Pablo64]

That is undoubtably one of his most quoted sayings. If I remember correctly, it shows up in a section of his book "Time Enough for Love" as being written in the notebook of the main character, Lazarus Long. Lots of other great quotes and such in that part of the book.