Wow, what a thread
Ok, last AC: I'm not sure what you mean by "merely using the work imposes a moral obligation" so I'll clarify my standpoint. Consider an open source project, such as Celestia, which I've downloaded and use a lot. Doing so places no moral obligation on me or anyone else to contribute to the project, or pay anything for doing so. Although - in resonse to another poster who accuses me of double standards - I HAVE contributed to Celestia and a couple of other projects that caught my interest. So don't tell me that I don't when you have no idea what I do.
Now suppose someone were to take the code for Celestia and turn it into a closed-source space game for which they charge say $60 and a $20 a month subscription, without releasing the source. Not only is that a violation of the GPL, it's morally execrable. It is THIS that I was having a go at, and I stand by what I said. If I contribute source to a project, and some company steals that source and uses it in a closed-source product, that is what I meant they can damn well pay me for. Not merely downloading and using the program, but reusing open source code in their own closed source projects.
Sorry if I caused any misunderstanding of my view there, I hope this clarifies things. If you still disagree with me on my stance, however, then I am opposed to your way of thinking.