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.