I sell software to the Chinese government to track down dissidents and kill them with drones. I release a lot of code under a GPL license and use the funds to promote OSS software. Most people wouldn't consider this a positive for the world even though more GPL software is created. Or in other words many people do not believe that "the ends justify the means" is a valid reason for something.
Essentially it boils down to this: if you see value to society in allowing people to share musical scores with each other, that's fundamentally at odds with a libre software philosophy. Because if you let people share music on a platform, they will inevitably share copyrighted melodies, which means not only that you are forced to monetize to be able to strike licensing arrangements, or else be sued into oblivion. And you are also required to enforce that the sharing software be used as intended in order to placate rightsholders, or else be sued into oblivion. And it's that "as intended" that is fundamentally different from how many of us think about FOSS.
There's a lot of corporate speak in the official post here related to the emplacement of score downloads behind the paywall in the first place https://musescore.com/groups/improving-musescore-com/discuss... but it's the same sentiment: if MuseScore.com doesn't put in place paywalls for downloads and enforce them, they will lose their ability to negotiate with major music publishers, and they see that outcome being a net loss to society of access to digital scores.
Frankly, I think this is a reasonable tradeoff. MuseScore sees monetization and adherence to these restrictions as a necessary step to ensure they have the resources and community to promote music literacy. That's a distinct mission from, say, GNU's mission, and just as valid. And of all the corporations using GPL for visions distinct from GNU's vision (here's looking at you, AWS), this one at least has a reason beyond being a naked cash grab.
The discussion stops being nuanced as soon as the company starts the discussion with a threat such as "will cooperate with github.com and Chinese government to physically find you and stop the illegal use of licensed content".
At the point the email in the Github issue was written the API was public. It was removed after the repository owner responded, as can be seen on the Internet Archive.
Nothing ever justifies offering a public API and getting people to use it, to only later backtrack, accuse users of "stealing" and threaten developers with use of physical force.
If the problem is caused by major industries, then just remove the previously public API and don't send mafia-like threats.
I think any reasonable person would find this unethical mafia-like behaviour.
