On telling others "proprietary software is bad for you", and the argument of reciprocity.

One argument that comes to mind when someone else asks me to help them with a computing task which involves using proprietary software is: I can't help you because "it is bad for you".
Which is strong. Some say that we are much better at knowing what is bad for us that what is good for us, therefore we should refrain from telling others "what's good for them". John Stuart Mill goes a bit further (as far as I can remember from my readings) and says something like: only take the liberty to tell others what *not* to do if you have reasons to think that their actions are hurting you. Which can be the case, I think, when others use proprietary technologies.

However, I feel that the argument "it's bad for you" falls short to convey a meaningful message to the ones who are insensitive to free software. And until recently I had nothing else to say that was striking enough to be perceived by others, in a day to day conversation, where the idea of free software is most likely foreign.

Another argument I have now, which I read about in the writings of Stallman, is the argument of reciprocity. One could say something along the lines of "If you ask me to help you with a task that involves propagating usage of proprietary software (thus helping the agents controlling of proprietary software), I won't help you because controllers of proprietary software will not contribute reciprocally". In other words, why shall I contribute to the propagation of proprietary software when controllers of proprietary software won't share their work freely (as in freedom obviously).

The (historical) example that comes to my mind about reciprocity in the software world is the one Stallman tells in one of his essays or in the book *Free Software, Free Society* (I don't remember). When Xerox asks him for a programme, which Stallman shares freely, but which Xerox refuses to "share back" when Stallman asks for improvements to be including in the original source. Xerox refuses: "it's proprietary".

Some philosophers talk about the unconditional need for reciprocity for society to sustain itself (Aristotle and others). And so, often, I think of the argument about reciprocity as stronger or maybe just easier to perceive that the argument "it is bad for you".

All of this to try to reflect on how to make it easier for others to perceive why copyleft-licensed software matters.

Thoughts welcome.