That's an unfortunate example, as defamation is notoriously difficult to prosecute as it requires proof of knowledge and intent, among other things.

The problem lies in how such a law can be used; unless the law is weak it will likely be abused (but then its effectiveness will also be minimal).

The issue with many laws is that they take into account the individual case.

If somebody has a track record of lying, it should be easier to prove subsequent lying.

Of course, then the potential for abuse is greater. It's about finding the right balance.