You're free to pretend there's a constrained license, and pay the project for their work. Are you saying you'd rather be forced to do so by a license? That makes no sense -- you can do it without being forced, if you want to.
I mean, I like copyleft licensing. But it's perfectly reasonable (albeit possibly naïve) to request commercial donations on a non-copyleft project.
If I use the software and make money, but don't donate, should I fear being socially reprimanded? What's the line there?
Piracy is one thing, but this borders on extortion and frankly would make me uncomfortable using this software.
It's a request, not a demand. And this project's maintainer is being more upfront than other projects.
The developer states the following:
> If you are using CodeMirror commercially, there is a social expectation that you help fund its maintenance.
Calling it a "social expectation" is frankly a pretty big turn off for me.