> They can, but it's often possible to prove it later. If you have a rule against lying and it's retroactively discovered to have been broken, then you already have the enforcement mechanism in place.
It isn't a rule against lying, it's a rule requiring lies to be labeled. From which you get nothing useful that you couldn't get from a rule against lying, because you'd need the same proof for either one.
Meanwhile it becomes a trap for the unwary because innocent people who don't understand the complicated labeling rules get stomped by the system without intending any malice.
> Really, your argument can be generalized to 'why have laws at all, because people will break them and lie about it'.
The generalization is that laws against not disclosing crimes are pointless because the penalty for the crime is already at least as severe as the penalty for not disclosing it and you'd need to prove the crime to prove the omission. This is, for example, why it makes sense to have a right against self-incrimination.
It isn't a rule against lying, it's a rule requiring lies to be labeled. From which you get nothing useful that you couldn't get from a rule against lying, because you'd need the same proof for either one.
Meanwhile it becomes a trap for the unwary because innocent people who don't understand the complicated labeling rules get stomped by the system without intending any malice.
> Really, your argument can be generalized to 'why have laws at all, because people will break them and lie about it'.
The generalization is that laws against not disclosing crimes are pointless because the penalty for the crime is already at least as severe as the penalty for not disclosing it and you'd need to prove the crime to prove the omission. This is, for example, why it makes sense to have a right against self-incrimination.