Uses & misuses....

[Neithan]

They used the quote because it's a darn good quote. It's that simple.

Exactly, Faramir's quote says what the author wanted to say (at least it does out of context) much better than the author could have said it him/herself. That is why it was used.
And another thing, is that particular use such a horrible perversion of Tolkien's intention? Granted he was talking about war but what is wrong with taking the same concept and applying it to individual protection. The only way that the use of the quote could be called morally wrong would be if Tolkien had said that he was for gun control but (to the best of my knowledge) he said no such thing.