The Netherlands has both. "Laster" requires the accusation to be untrue. "Smaad" is the broader form that does not require the accusation to be untrue.

Justifications defined in the law are "necessary defense" and "common interest". The second one is specified as "believed in good faith that the charges were true and that the public interest required the charge." IANAL, but I think this can apply to social media witch hunts to at least some extent.