[dale_glass]

They become grim because the conflict is asymmetric.

Slinging insults, hate, disinformation, or just posting plain nonsense is easy. Explaining how things work properly takes a lot of effort and is hard. Eg, saying "The moon landings were a hoax" is easy. Explaining why that makes no sense, and how exactly humans did land on the Moon takes a good amount longer.

There's also that the valuable, accomplished people in a community are a scarce resource. What would you prefer the resident rocket scientist to do, provide useful information for the community on something new going on, or try to reason with the newly arrived conspiracy theorist?