Am I responsible for something

someone else says or does?
There has been a recent court ruling here that someone who is described as a "serial political candidate" must pay damages because he not only defamed someone on his Facebook page but he also allowed others to do the same thing.
I haven't read the actual reasoning of the judge and the matter will certainly go to appeal but it should raise alarm bells. If the judgment is upheld then it would bring social media and news websites to a juddering halt.
I would seriously contemplate no longer writing this blog.  It would not be because I plan on defaming anyone. I hope I have never done that. The problem is that I could not take the risk of being held responsible for the actions of another person - actions over which I have no control.
Some months ago someone I know was accused of committing a serious criminal offence - using a "carriage service" (in this case the internet) to "malign" (defame) someone else. There was no truth in the accusation. It is actually highly defamatory. Those responsible for making the accusation may well not have been fully informed when they made it. Almost certainly they simply believed what they were told by someone else, jumped in and made the completely unwarranted  accusation. An expression of genuine concern for someone else was simply (ab)used in a way it should not have been. It has done untold harm to an individual and to a group but the damage has probably been largely limited to them. Still, the damage is there. You can't take words back. 
But who would be responsible if it had ended up on social media? What if it had ended up on a "closed" group on Facebook? Would the court say that the publication  was "limited"? How could it be when anyone belonging to that group would be able to pass the  information on?
News sites like those belonging to major media groups often allow public comment. They are supposedly moderated but the reality is that a lot of defamatory comments do get through. Words get twisted - and some serial commenters are masters at it - and people get hurt.
Is it the price we have to pay for being able to use the internet - or do we try to stop it?
The ruling in the present case is likely to be complex. Defamation is a very complex area of the law, one I know very little about.
What I do know is that you can't take words back - and of course there are times when I would have said things differently too.