There are times when a copyright is the sensible thing to do. When you’ve put a lot of effort, time or money into a production, it only makes sense that you should get a return on your investments. Communication is important, but sometimes – and particularly with entertainment – it takes a back seat to getting paid.
There are other times, however, when the idea is more important. When it matters more that you communicate than that you renumerate. There’s any number of reasons why, but mostly they come down to you wanting to get the idea out there more than wanting to get paid. (Not that getting paid isn’t nice.)
It’s for times like those that Creative Commons and other such organisations exist. They allow you to pick and choose the legal protections you want, rather than the all or nothing options of copyright and public domain.
It’s worth keeping in mind that in the 21st Century, we have a few more options than our predecessors did – and it’s worth using them when they’re the appropriate choice.