> Unless the drive-by PR is fixing a simple bug in a simple way, then the contributor really should've opened an issue first. Doing otherwise is rude imo.

I kindly disagree. If the project is open source, it means that I can fork it. If I find an open source project and want to add a feature to it, I will fork, implement my feature, and then open a PR to the original project. A couple things there:

1. I have no need to open a PR to upstream, it's totally right to keep my changes in my fork (as long as I honour the licence).

2. If the maintainers don't feel like merging my PR, they don't have to. It's their right. They may request changes, and I may choose not to implement them.

It's not the only way to do it: it's perfectly fine to open an issue and ask for guidance. But I don't see the problem in opening a PR saying "look what I did with your project: you can merge it if you want".