There is a clear difference between saying not to do something because it's immoral, and saying doing that thing would be futile.

In the Sopranos, there's an episode where a coffee shop protection racket is ruined because a local shop is replaced by a corporate chain that accounts for every cent daily, and immediately fires any employee involved in a discrepancy. In this case, the theft was prevented not by convincing the mobsters of the immorality of their actions - they simply had their harness replaced with one that no longer facilitated the bad behavior.