I know quite a few open-source maintainers who have never showed any kind of hostility, even in situations which would warrant hostility.

That's great for those developers but you can't expect everyone to act the same way. The fact is that you have not right for ANY support - there is even a disclaimer for that in pretty much every open source license.

I'm not talking about rights, I'm talking about manners. Everyone has the right to communicate any way they want, but I also have the right to call them out on that.

If you have a public, open-source project on GitHub, and you regularly accept and respond to issues/pull-requests/suggestions, you are obviously presenting yourself to the world. It is basic courtesy to not be hostile in such communication.