Your analogy is bad.
"Some little on-line forum" with a few angry users is not really comparable to a mega-corp with billions of users.
Lawyers could but are unlikely to go after a few misguided individual users for slander. As they say, you can't get blood out of a rock. Mega-corp is a much more tempting target.
Legal liability for bad AI is just getting started but I expect lawyers are giddy with anticipation.