Constructive feedback shouldn't be angry nor emotionally charged. That's just bad feedback.
I also don't think constructive feedback is super rare either. But I guess it depends on the project. eg some projects might have an appeal to different communities who are less often less patient with maintainers.
I think it's also worth remembering that maintainers do also need to be patient with the community. Sometimes I've seen maintainers not handle themselves well even when that feedback is PR fixing a bug or security vulnerability and there's no comment, suggestion nor anything else about the existing code base. In those instances you either just have to accept the maintainers vision (even when you disagree with it) or fork their project and maintain it yourself (which I've had to do before).
Ultimately though, most people I interact within OSS are friendly enough.
I also don't think constructive feedback is super rare either. But I guess it depends on the project. eg some projects might have an appeal to different communities who are less often less patient with maintainers.
I think it's also worth remembering that maintainers do also need to be patient with the community. Sometimes I've seen maintainers not handle themselves well even when that feedback is PR fixing a bug or security vulnerability and there's no comment, suggestion nor anything else about the existing code base. In those instances you either just have to accept the maintainers vision (even when you disagree with it) or fork their project and maintain it yourself (which I've had to do before).
Ultimately though, most people I interact within OSS are friendly enough.