So I've caught up a little on this situation and to summarise as I understand it, there's a dude who is admin on a site where many people have contributed their work under CCv3 licence. This dude started banning people who questioned his political stance and began to behave very erratically and having meltdowns. He's now trying to stop people archiving the site content.
So I'm not so much on the technical side of this but I am interested in the law. The entire site is a MediaWiki instance - public Open Source software that he didn't write. As part of the software's design, it offers both user-facing web pages and technical interfaces, an API that allows the content to be read as XML (a text-based technical format).
His entire site is licenced under the Creative Commons Attribution licence v3. This licence explicitly addresses Technical Protection Measures". Specifically that under the terms of the licence you may not introduce them for the purposes of restricting access. This doesn't cover traditional username and login but then the site is public access without username and login so that exemption doesn't apply. It doesn't require you to ensure everyone has access, but it does require you to not take active measures to interfere with access.
Reading his tweets above, he is actively altering the normal functionality of MediaWiki in order to explicitly prevent accessing the content - he admits this. It has nothing to do with the DDoS which I don't know much about, he's blocking archivers "scrapers" as he calls them to prevent people accessing the data for purposes he doesn't like. But it's not up to him to decide that, the licence he has chosen to use forbids this.
And he cannot try to make it about resources. A request via the API for a current XML version of the page consumes less resource than a browser request for the same page in HTML. Both in bandwidth and computing resource. He's violated the licence terms that he has promised to the contributors to the site.
Some links and excerpts:
So, who can act on this? Well technically anybody could. You reading this right now could. There's not really much legal leg to stand on. And there's certainly not any moral leg to stand on as the whole point of the creative commons is to allow the easy sharing and building on each other's work and MediaWiki by design is intended to share the information in easy ways including programmatically. All he's currently doing is stopping other people backing up or sharing the contributor's work. Something contributors have implicitly given permission to do under the licence.
But specifically as to who can act on this, any site contributor is entirely within their rights to demand that he comply with the terms of the licence they submitted it under. And honestly should. If you have put time and effort into making this content and releasing it to the public, you don't want it in the hands of someone who appears to be having a melt down and actively treating it as if it's his.
So long as attribution is preserved, and that only applies when re-publishing it, he has no footing here. He's acting like the creative commons material entrusted to him is his. But it's not - neither by letter of the law nor spirit. The guy can't profit off Open Source and CC material when it suits him and then pretend it isn't when it doesn't.
He's putting more effort into preventing people archiving the site than running it. Again, in his own words. Power mad it seems to me.