If you are developing open source software, the bevy of open source licenses you have to choose from is rather enormous. You have choices of everything from Public Domain to GPL to Dual licenses, etc.
And that is a good thing. While making choices is hard, having a choice is always a good thing. And in the case of open source licenses, the plethora of options provides you with opportunity to decide how your software impacts other developers and corporations. The two licenses I run into most often are the BSD license and the GPL license.
The BSD license is about user's freedom and author's credit. The user has the right to do anything and everything with the licensed material. The only restriction is that the original author gets credit for the original author's material.
Think about it this way. BSD promotes free-trade and constant exchange of ideas based on individual freedoms and values. The market place in this free-trade economy is populated by the developers of the world. The copyright holder or licenser has no power or authority to require tithe or change-sets. Under the BSD license the world becomes a free market where ideas are free to be used in any way possible.
In contrast, the GPL license is about the material's freedom. The user has the right to do anything with the licensed material as long as he makes an attempt to put all of his changes and usages into the open source community.
The GPL license was designed to make sure that open source code never finds it's way into proprietary software. It takes away the end users freedom to attempt to make improvements for personal gain; however, this loss of individual freedom comes with the benefit of an empowered community. All of the developers can rest assured that their code is not going to disappear and become closed source.
So in summary, the BSD license is not "promoting" proprietary code. It is promoting real individual freedom and opportunity. The BSD license can be considered anarcho-capitalism's equivalent in licenses.
The GPL license does not promote individual freedom, it promotes a community around the good of all. The GPL license can be considered socialism's equivalent in licenses.
Think about what kind of impact you want your code to have on the world, and make your decision based on that. And remember, no matter what license you choose, the copyright holder always has the power to change their mind.