As Phil says, we already have defamation laws that draw similar distinctions. For instance, in many jurisdictions a statement can’t be defamatory if the person making it made it in good faith and reasonably believed it to be true.
In those cases it’s a kinda-randomly-chosen jury, guided by a court proceeding with lawyers on both sides and a judge in charge, that has to make the call. We as a society seem to have decided that that gives fair enough results. Maybe it would work much less well for an offence of spreading malicious lies (because maybe it would be more tempting for governments to put pressure on the courts, or maybe it would more often happen that the jurors’ political prejudices got in the way of making a reasonable decision) but it’s at least plausible that it would be net beneficial anyway.
As Phil says, we already have defamation laws that draw similar distinctions. For instance, in many jurisdictions a statement can’t be defamatory if the person making it made it in good faith and reasonably believed it to be true.
In those cases it’s a kinda-randomly-chosen jury, guided by a court proceeding with lawyers on both sides and a judge in charge, that has to make the call. We as a society seem to have decided that that gives fair enough results. Maybe it would work much less well for an offence of spreading malicious lies (because maybe it would be more tempting for governments to put pressure on the courts, or maybe it would more often happen that the jurors’ political prejudices got in the way of making a reasonable decision) but it’s at least plausible that it would be net beneficial anyway.