There's a huge wave of open-licensing sweeping the 'net, and it's starting to get into the real world. This is definitely a good thing - freedom of information is a great. The most common licenses, such as the GNU FDL, or the Creative Commons BY-SA stipulate that anyone can use the works, as long as they acknowledge the author, and that they keep it free (usually by using the same license). The last tactic has been called "viral" by numerous capitalists, and they are correct, it is. Eventually it will take over the world, or at least a large part of it. I can't wait.
Creative Commons, and perhaps a few other licences, give people the option to license their work with a "non-commercial" (NC) clause, This is strongly derided amongst the free software movement particularly, as economic exploitation by a creator is considered a freedom and a right. This is argued well on the Freedom Defined wiki.
There are two main arguments against using an NC license, the first is economic, the second in a matter of compatibility. A third minor argument against the CC-BY-NC-SA, is an argument against creative commons itself. I will deal with these in the above order.