Comment is free, facts are sacred wasted.

The world is now drowning in opinions. Facts, meanwhile, are not having a good time. They are expensive and time-consuming to establish - and there is growing evidence that people are losing faith in the idea of agreed objective truth. Big tech has decided that public notes are more valuable than fact-checking. How did it come to this - and what is the way back?

Moderated by Alan Rusbridger.