Legal threats regarding internet forums have been shown to be 99.99% utterly and completely vacuous - all bluff and bravado. True, they are levelled regularly, usually when someone is losing a particular argument or feels aggrieved that they've been caught out. But there is a significant onus and cost on accusing someone of 'libel', especially on the internet.
Just my two-bobs worth coming from my crass, lower-class, uneducated and rebellious-against-the-empire convict heritage (actually, we were pure English settler, but never let the truth ruin a good story).