Libel doesn't have to be false, just damaging.
http://en.wikipedia.org/wiki/United_States_defamation_law "...the truth should be an absolute defense against libel charges." "Also, the truth of the allegedly defamatory statement will always negate the claim (whether because the plaintiff fails to meet his/her burden of proving falsity or because the defendant proves the statement to be true)." The second quote implies a burden of proof upon the plaintiff to prove the statements false, although the main wikipedia article on defamation also mentions publishing with reckless disregard for verifying the veracity. Dunno if that second category applies in the US.
Libel lawsuits in England are similar to patent lawsuits in Texas - you know that the venue was chosen mainly because the person filing the suit wanted the friendliest court possible.
The freedom of speech devices in the Constitution prohibit anonymity, rendering themselves ineffective.