Flamewars notoriously have that feature, like a black hole dragging in more and more participants until everybody is Hitlin-Staler.
I would <personal opinion incoming> that most modern news websites and television news channels are toxic because they make the viewers more neurotic and in a way that spreads because misery loves company.
I suspect that a ban on news would magically improve social networking. People would still talk of news but the toxicity would go way down. No exceptions, total ban.
If a nuke goes off or the zombies are coming - you'll find out somehow.
Sometimes I miss out on daylight savings time changes or something basic everybody appears to know and I'm fine with that. Some people will think this impedes some democratic process - I can't imagine what happened before 24 hr news was invented or the television, I'm sure it was a complete nightmare.
So, when "toxic" is used to the exclusion of actually describing what happened you have to ask yourself: why isn't the speaker communicating more clearly? Maybe they're bad at stating their point, maybe it's a loose informal conversation, or maybe they benefit from the information asymmetry.
Toxic always brings forth memories of either Ninja Turtles or Swamp Thing, for me though.
It means exactly what it says on the tin.
It is a bit like the word fascist which used to have a specific meaning, but which has been so widely applied that it is now pretty much meaningless except as a term of abuse.
"This gaming community is toxic" could be read as "This gaming community is extremely obscene"
"This forum is toxic" could be read as "This forum is extremely negative"
Seems to match the usage I see anyway.
To answer your question toxic no longer has a real meaning outside of science and medicine.
Iseendai's "Sick systems: How to keep someone with you forever" post: https://issendai.livejournal.com/572510.html
which is about abusive and exploitative relationships / organisations / businesses / cults . probably a bit of a tangent, but perhaps a more useful one to read and think about.
* probably as a result of mentally associating hackernews ~ software jobs ~ bad software jobs ~ abusive/exploitative workplaces ~ toxic relationships ~ "toxic"