Did I hear someone say; “What is truth?” It’s a pity to live in a time when people so often quibble at details to avoid dealing with the larger issue.
I believe in the simple case that overrides the boundary conditions – so I believe that we can discuss “truth” and “lies” as human actions that directly affect people – without prejudice to the finer shades of their character.
Why expose the truth; instead of just the lies, or the liars? For the same reason that people use constructive criticism: to build a path to something better.