I don't understand your question.

Maybe I'm misunderstanding your point then. I got from your posts roughly: It is unethical for end-user software to be closed source, everyone is fundamentally entitled to the source code for programs they run on their computer. Further, if an end-user decides not to run the closed-source software, it is still unethical because many people don't understand the value of source code and they are still being exploited when they purchase/run the software.

My question: Is it still unethical if the exchange and use of proprietary software is made only between people who fully understand the value of source code and decide to anyway?

It's a potentially unethical situation at the very least.

If the person running that software asks for the source code, it would be unethical to withhold it from them. However, from the arrangement you made, it would also be unethical for the person to exercise that entitlement which they previously agreed to give up. Two unethical actions don't make a right, so you're just setting yourself up for an unethical situation all around. Better to just make it clear the source code's available on request from the beginning.