The amount of FOSS in the world that exists from people who contribute on their own time is a small fraction of the amount of software (total) in the world. Yes, software won't die out, but if somehow people couldn't get paid to be software engineers any more, there would be a lot less software engineering happening.

It's certainly possible to argue that copyright is so bad that we should have way fewer authors and musicians in this world, such that only those who are truly passionate about writing and making music (and/or independently wealthy) will do it, but it doesn't seem to me that that's what people are arguing.