Yes, if nobody could get paid for writing code, there would probably be less of it. (Barring some sort of post-scarcity economy, I guess.) However, your origin

Yes, if nobody could get paid for writing code, there would probably be less of it. (Barring some sort of post-scarcity economy, I guess.) However, your original assumption does not flow from the premise--just because selling software becomes impossible does not mean programmers won't get paid. I recall reading somewhere (too lazy to find the source) that the majority of programmers work on bespoke, in-house software rather than consumer-facing proprietary software. Even if it is not a majority, it still shows that there are viable ways for programmers to get paid outside creating scarcity with copyright. Just because people contributing to the kernel get paid does not mean they would not get paid without copyright. Companies like Google and Red Hat do not really rely on copyright for money.