This attitude reminds me a lot of Stallman, and honestly, I fundamentally disagree with his absolutism about the ethics of being paid to write closed-source software.

Sure, there are many people who are happy to write software in their spare time, and are sufficiently well off from another income stream that they can afford to not profit from the software they produce (although I suspect that the vast majority of open-source programmers also derive their primary income from closed-source software).

But a simple fact of life is that people need to eat, find shelter, etc, and it's reasonable to expect that if you have a particular skill that others don't that you should be able to exchange the products of that skill for money from the people who recognise that skill and want the products of it (whether it be software, books, artworks, music, whatever).

Sure, there are some people who would continue producing the art/writings/music anyway in their free time because that's what motivates them in life. But what a shame it is when someone can only do that for a few hours per week because they need to work a full time job which doesn't utilise their talent just to put food on the table. Perhaps they'll choose to live a meagre life, and work for the "sake of subject" and die in poverty, but most won't. That doesn't reflect on the quality of the work, just how much hardship the creator is prepared to endure.

I'd never heard of Arthur Schopenhauer before, but reading his Wikipedia suggests that he came from a wealthy family and he never had to worry about money. Perhaps his argument just boils down to class at the end of the day, and that only authors from a well off background should be given a voice. But like I say, I don't know anything about him and he sounds like a well regarded philosopher, so I'm probably well off base.