I'm not much impressed with the thread title, either.
Being 'polite' really isn't all that difficult, you know...
volsung.....the spoken word is 'transient', requiring an immediate audience, whereas the written word is accessible for a greater period and a wider audience.
That being the case, I think 'libel' is more correct for a message board, where the statement is, or can be publicly available for days or more....