Also, it is considered polite to ping a Freeper you are quoting. However, in some cases (e.g. the poster asked not to be ping) it is a way to respond without confrontation.
Let's look at a hypothetical:
FReeper John Doe is a member of the Church of Funny Math and continually says that Catholics believe that 3+2=7. Every time he says this, several Catholic FReepers correct him and tell him that the actual answer is 5, but still he persists and even has a ping list of Funny Mathites who tell everyone that Catholics believe 3+2=7.
Why is it unacceptable for Catholics to say that the notion that Catholics believe 3+2=7 is a LIE even with the implication that John Doe and the other Funny Mathites have an intent to deceive?