Few works are released directly to the public domain. It is my understanding that the public domain doesn't even exist in all legal jurisdictions.

Most people license out the software under specific requirements and prohibitions. BSD requires attribution. GPL variants require adherence to copyleft when distributing derivative works. A little under half of all github repos don't even have a license, which means that though the source is published, no one has any license under which to copy it or derive new works from it.

So far as I have seen, whether aggregating and munging these works into abstract LLM weights constitutes fair use is still legally unclear. If not deemed fair use, it is almost certainly a massive violation of copyright.

You can read code, rewrite the functionality yourself, and sell it, and not be at odds with copyright. Open source does NOT protect against reimplementation. See Java lawsuits.

If you don't want your code to be used as possible inspiration, then you are not actually for open source, and are using the wrong license. The licenses are legal bindings, not moral bindings.

"Don't use any concept found within this code" would be a license that doesn't really fit with any current copyright law, and it wouldn't allow any software to exist, except that made in the 70's.