If you share your code with me under a copy left license, I will share my contributions under the same copy left license... you will not then be free to ask for money for things built on top of or with my contributions. You may be okay with that, but it is a decision you have to make.
A common misunderstanding with the GPL and other copy left licences is that they care about money and monetary transactions.
They mostly do not.
They only demand that you offer the source code to anyone that asks for it if you also distribute any kind of executable (you may even charge to cover the costs of the distribution).
The AGPL expands this to SaaS's too to close that loophole.
Sorry, I am aware of this, I worded my comment incorrectly. What I meant to say is that one will be unable to ask for money for a ~different license~ to my contributions, becuase my contributions will be under the copyleft license, and I will not sign any agreements that give the project maintainers rights to license my contributions under a proprietary (Non open source) license. Yes, anyone is still free to ask for money for copy left code. But it is still copy left, and as such, the license goes with it.
