Without IP how can you enforce copyleft? Someone could just take your code and modify it and distribute modified binaries without you being able to do anything.
Even in a post-IP world you can have it be law that anything sold must include its documentation, manuals, and thus in the case of software on the sold product, its source code.
The fact so few realize how grossly unjust it is that most products sold today not only are undocumented but are intentionally obfuscated to make repair nigh impossible in order to drive replacement is the origin of the problem, though.
You can, for example, reverse-engineer these binaries or develop binary patches (without IP laws, all of this becomes legal).
I could, for example, modify any piece of software I like, and legally distribute modified copies to others. Even if I didn't want to share my modifications with a larger community (or didn't want to do it for free), I couldn't stop it - someone else could do that for me. And as 'wolfgke points out, being open source doesn't matter much here.
No, without copyright, you cannot force the other party to give you access to the original source code.
BTW: There does not seem to exist an open source license that tries to emulate "no copyright"/"no IP". I.e. the license allows reverse engineering of all binaries derived from it virally, create modifications etc. and perhaps allows to use patents; but the license does not give you the right to demand access to the original source code.
At least the copyleft defenders would not agree.
Buddy, you must never have worked with a decompiler. To say nothing of the source file structure and comments that are lost along the way.
GPL requires source code, which it defines as "the preferred form of the work for making modifications to it."
This prevents release of compilable-but-obfuscated code, or transpiler output, etc., or intentional removal of information required to build the software (though this clause causes GPL-compatibility issues with authenticated-build platforms).