The reasoning behind Kerckhoffs' Principle is compelling. If the cryptographic algorithm must remain secret in order for the system to be secure, then the system is less secure. The system is less secure, because security is affected if the algorithm falls into enemy hands. It's harder to set up different communications nets, because it would be necessary to change algorithms as well as keys. The resultant system is more fragile, simply because there are more secrets that need to be kept.
Here is a very interesting article about the Kerckhoffs principle. This principle is related to the obscurity vs public security policy moot which divide some security companies and open source projects in their conception of what is the more secure.
It's a good and intelligent argument.