I understand where this thinking comes from but I still think it's kind of a simplistic attitude. People depend on the technology they use. When you convince someone to rely on something you've produced (and, crucially, continue working on), I think you do actually create a duty to be responsive to them. They depend on your work. Are we really so limited in our ethical thinking that we require an exchange of money to create obligation?

I understand that people can be aggressive, rude, and downright hostile. I'm not suggesting that such behavior be rewarded. Nor am I suggesting that every open source project has to do everything any user says. I do, however, object to the notion that there is no obligation whatsoever between the producer of a technology and the users of that technology, regardless of whether money has changed hands.