I don't understand people who like containerization. So now instead of just taking on the onus of maintaining a software library, now I'm going to have to fuck around with maintaining how I expect it to be deployed, and force other people to adhere to that model, thereby forcing my paradigms and alternate system architecture/exotic filesystem and concomitant weirdness onto the user?

I don't know, it just never clicked for me. Seems like a solution that appeals to people who like spending most of their time in config/build files than actually using a system, but maybe I'm just a curmudgeon/haven't used it right.

Docker is for applications. Using it in an actual library for a programming language should be limited to setting up the dev environment needed to run tests [for the benefit of consistency]. It makes sense for someone like Discourse to only support running via docker since they want to make sure you're running with the exact same dependencies they're running with which makes issue-reporting and debugging easier.