I'm concerned about DRM violating my rights. But apart from that, media is largely for consumption, there's very few reasons to need to edit a movie or something, and the laws at least attempt to cover fair use. DJs remix songs and stuff just fine. Or news article, you'd mostly want to quote them which is well defined in the legal framework. It's important to remember that open-source doesn't imply free of charge: there is paid GPL software.
Open-source is important in software because it's much more complex, and you can end up in a situation where software you bought doesn't work because the company refuses to fix it, or straight up stops working because the company went bankrupt 10 years ago and things have changed too much. Proprietary software is a black box that can be doing literally anything, and legally, you're not even really allowed to reverse engineer it to even make sure it does what it says it does.
Stallman started the free software movement out of frustration with a printer driver that he knew how to fix, but the company wouldn't give him the source code so he could fix it, and I believe at the time it would also have been illegal to reverse engineer it and patch it, or at the very least it was against the license. And that's also my reason for using open-source software: not because I want free stuff, but because I want libre stuff that I can fix and maintain. Most people won't, and that's where the sharing clause comes in: someone else that can patch it will, and everyone can just use that.
Ideally things would be free and widely available but that's too commie for most people and we're headed in the polar opposite direction. Buuut there's always the high seas where you can set your own moral compass.
If you look at it from a different angle and ask: who might be interested by a user being reported, given that each instance operate independently? The answer is all of them.
The rest comes naturally: obviously if the account is banned at the source it's effectively banned globally. If it's banned on the community's instance, then you won't see that user there but might on other instances. And your instance can ban the user, in which case they're freely posting on other instances but you won't see it from your perspective.