> "Do you really think that the stability, low cost and quality of Open Source software is independent of the Free Software ideology?"
Well, I do. Open Source is basically just Economics.
An initial release of source code happens because there's often no (more) alternative usage for it. From a product point of view, it's often unfinished. Turning it into something that could have an alternative use -- such as being sold as Closed Source Software, for example -- usually requires additional efforts; additional investments of time and money. Another reason for releasing the source code is the "death" of former Closed Source Software: Either it was killed by competition or because people's wants and needs changed. No or little future profit is to be expected.
In both cases holds: The opportunity costs of releasing the source code are low or even zero. One looses nothing by releasing the source code. If you'd loose something, you simply wouldn't release it. And every Open Source advocate is fine with that.
As for contributing to Open Source: It simply pays. If a developer is sufficiently annoyed by a missing feature or a bug to justify make a patch, it will happen. It's pure self-interest. It's economic behaviour.
The next stage is the more important one: Why send the patch upstream? That's simply, again. First, the opportunity costs of sending the patch is zero, again. The developer couldn't use the code of the patch for anything else. Second, sending the patch upstream, will save him effort. If he (or she) wouldn't send the patch, that's basically a fork so he or she would have to waste his time solving conflicts, etc. Sending the patch upstream is, in most cases, pure self-interest. It's economic behaviour.
Accepting a patch is usually also rational, for it improves the source code for the original developer.
In other words: each stage of releasing initial source code, making patches that fixes bugs and improves the functionality, and accepting these, is entirely self-interest and economic behaviour.
No need for any ideology.
Your argument that Open Source wouldn't exists without Richard Stallman, is basically useless: How could we know whether it wouldn't? It's an empirical question that cannot be tested with an experiment.
However, we can make some analogies: Solutions are often invented when problems exists. In nature, the eye was invented several times independently because it helped the creatures to survive more often.
So, it seems save to say: Without Stallman, something like Open Source would have been invented by others. In fact, Project Gutenberg -- free distribution of classic texts -- was invented in 1971, already. The first BSD "distribution" was assembled in 1977. Several others released source code without ever having heard about Stallman and Free Software, before.
Again, no need for any ideology.