One interesting thing is the FSF’s principles have absolutely no problem with a free engine and paid assets. They explicitly say they have no position on artwork and I’d say art, sound, level design, and so on all qualifies as artwork. That arrangement looks like a good one to me. It leaves plenty of room for the seller to make money while respecting user freedom. And every case I know of where a mod community thrive…
Right, the FSF has always had the view that software developers are the only creative professionals who must be shamed for not releasing their hard work for absolutely free. Authors are allowed to hold copyrights on their books, artists on their paintings, musicians on their music; but programmers? Fuck them if they even THINK about trying to maintain control of their creative outputs -- they're clearly evil. J.K. Rowling is allowed to make money on Harry Potter, but you're not allowed to copyright your code.
And can it with "but these 47 people in history have all managed to make a livable income from consulting based on their open-source work!". That's just more of you telling me how I'm supposed to live. I don't want to make money helping incompetent companies install the software I wrote. I want to make money in proportion to the value I add to the world.