Yes, of course, works that are no longer copyright can be used freely, and that applies to all art. Usually it’s about 70 years after the artist’s death, I believe (I’m not an expert in copyright law), but there are some exceptions.
I do agree with most of what you’re saying - most art is derivative and is usually influenced by earlier works or styles, and many phrases and modern works have their origins in historical writings.
I disagree that it’s ‘the entire poem, song or novel that’s the artwork’ - that would imply that I could copy and sell a verse of a poem, or a chapter of a book, or a section of a painting as long as it wasn’t the whole thing. I’m not sure many artists would be happy with that. Where to draw the line is difficult - should it be a whole verse, a whole line, a few words?
Yes, it does all come down to money - but that’s exactly why people want to use these popular phrases…to make money from them. So is it the artist that is being greedy in protecting their work, or the copyists who are trying to make a quick buck by ‘stealing’ someone else’s ideas?
Personally, I’d rather stick to being as original as I can (ok, I know there’s nothing really new in the world - it’s all been done before!) and keep away from anything that I know is copyright-protected.
