I'm not a Lawyer, the view expressed below is my own.
We see everyday new Crypto software. From IM Applications to Secure Storage programs, and many more. Crypto now a days is a vital part of our time spent in front of a PC Monitor.
Almost every site you visit on your Browser and App you use on your Smartphone use (or should use) Strong Cryptography because Crypto is not a crime
But, with Crypto also comes Trust. It's easier to trust an Open-Source, Audited software that a Proprietary one. (Stay away from self-proclamed "Military-Grade Cryptography" and "Snake oil")
So I will explain why in my opinion is better license Crypto Software under GPL.