With respect, Ron, you're missing the point.

First of all ... it's not "may". The enemy (or "some of them", as you now say) has your "playbook" with a high degree of probability. Shall we talk again about TSA's SSI documents that have been posted to the Internet? Even if they don't have the actual documents, your enemies can certainly determine the contents of the playbook simply by performing test runs through the checkpoint and watching how they are screened.

Yes, no security system is perfect. By fully publishing the plans of your security system, you open yourself up to the possibility of your enemies trying to find ways to beat the system. You also open yourself up the possibility of your friends trying to find ways to improve the system. And you have more friends than enemies; odds are in your favor that your friends will find ways to make things better faster than your enemies will find ways to tear your down. You also remove any possibility of self-deception: believing that your rules are secret when they aren't.

I find it fascinating that the most sophisticated encryption algorithms in use today, like AES, are publicly-known algorithms. Even though all the details of AES are publicly known, the Feds use AES for all levels of encrypted communication. They aren't bothered by the fact that the enemy knows how they're sending messages. Instead, they've chosen to use a technique that is still incredibly strong, despite its public nature.