As JWs, we weren't witnessing online, but in person. We act differently when communicating face-to-face than when we communicate online. It isn't unique to JW boards either. You could have an online forum about knitting and the same phenomenon will occur: sniping, arguing, insults, etc. Put those same people together in a restaurant for lunch and they will get along fine.
We haven't forgotten what we learned as JWs, we are just in a new environment that
inevitably leads to more fighting than in person. Something about the anonymity, and other sociological factors.