Person 1: I have built this thing, maybe somebody finds it useful. Then you can have it for free.
Person 2: I'm not going to use it unless you do as I say with your thing, and I'm not going to offer anything for you.
Well okay, then don't use it? Or if you want a feature, offer something in return. Or make the request towards a paid service – their ears are very eager to hear what features potential customers would like to have.
You have a cynical view of what is a feature of Show HN posts: community feedback. This is where the rubber meets the road and where you find out if people would use your project. And part of that is people telling you why they wouldn't use it.
The best case scenario really is that the only thing keeping someone from using your project is a feature that you can implement that would make your project better for everyone. For the sake of launching, you tend to pick a subset of features that you consider necessary, and it's good feedback when all you need to do is extend the circle to include a few more.
I think your negative reaction is warranted for when people trash the project, especially under the weak guise of constructive criticism. But feature feedback is not that.
The OP himself liked the feature request which is perhaps a counterpoint to your interpretation. I don't think they would agree with you that it was inappropriate nor demanding, but rather useful feedback.
One of the problems with open source hobby projects as opposed to projects you do for a job is the lack of feedback. If I ever were motivated to do an open source project to scratch an itch, I would want feedback and feature requests to make it better
Person 1: I have built this thing that I hope you find useful.
Person 2: I can't use your thing unless it has this feature that my current thing has.
That is a two-way interaction, not a one-way demand. Person 1 is enriched by understanding what features might help them build a product people want.