@NoOne phil,
You must have misread my post. I agree that judgment is a wavy thing and not to be relied on. So, I advocate following the black and white laws of internet use to the letter.
I'd feel ok banning for these:
"Bob, I'm coming to Fresno to punch you in the face."
"Hey, let's set fire to the Federal Building Thursday."
"I wish the Samoans were extinct. Every ******* Samoan I've ever known is a waste of flesh." (wait, I'm not sure this is illegal...)
"These are my sexiest pics of child porn. Feel free to download them."