It may be possible that they organizations and companies will be supplying these devices, nevertheless they will still have more control over who is allowed to access these networks. This in itself can help to reduce the frequency and quantity of security breaches.
Concerning network security if companies do include BYOD practices in their employment techniques they do exercise more control over what is accessing their networks. This brings up another question of whether the employees of a company will want to submit their personal devices to corporate regulations, or if they would even want to use company infrastructure.