The optimal amount of crime in a society is non-zero because a society with zero crime would be a dystopian police state where innocent people sometimes get caught up in the justice system's net to make sure it catches all of the criminals.
The classic principle of Anglosphere common law is that its better to let 10 criminals get away with it than to convict 1 innocent person. The same idea applies to fraud because overzealous fraud prevention causes problems for legitimate users whose actions incorrectly get detected as possible fraud. The benefit to tolerating a low amount of fraud is that your product won't be hostile to your legitimate users. The benefit to tolerating a low amount of crime is that you will live in a free society rather than a dystopian tyranny. Freedom is good and it is worth giving up quite a bit of safety for the sake of being free.
The classic principle of Anglosphere common law is that its better to let 10 criminals get away with it than to convict 1 innocent person. The same idea applies to fraud because overzealous fraud prevention causes problems for legitimate users whose actions incorrectly get detected as possible fraud. The benefit to tolerating a low amount of fraud is that your product won't be hostile to your legitimate users. The benefit to tolerating a low amount of crime is that you will live in a free society rather than a dystopian tyranny. Freedom is good and it is worth giving up quite a bit of safety for the sake of being free.