I get blocking users from opening/commenting/sending PRs/editing the wiki, but why block them from forking a public project?
People here don't get that some organisations and individuals will use it to push block lists, unrelated to any Github activity, and depending on your actions on Twitter, Facebook G+ or whatever you'll be blocked in advance from forking, contributing, interacting with a large range or repositories ... same as Twitter Block lists ...
Also, this feature already existed for individual accounts, for years, and worked that way. I haven't heard of blocklists for GitHub ever existing. Why do you think this is different for organizations?
It's OK for admins to deny pull requests, but not OK for them to deny the right to fork the said open source project. Kind of takes the open out of the open source by doing so.
If they block me preemptively, I can decide to investigate alternative projects to invest time into, or perhaps I can decide to fork the project (any free software or Open Source license requires non-discrimination in licensees), git push it to my own account, and attempt to run a non-abusive community around it. Or perhaps I can decide to reimplement it myself.
On the one hand, it's easy to see how this is a powerful tool respectful developers can use to moderate their community positively.
But from the other, I've heard a few too many stories along the lines of "passionate contributor breaks into argument with passionate repo owner" and chaos ensues. I could see feature a way for people to step on toes and divide rather than encourage positive community.
This has a fairly long history in the F/OSS community, partly out of necessity before tools like GitHub existed. If your project is owned by some organization like Apache instead of by you personally, you still get to be a maintainer, but there are well-defined procedures for you not being the only maintainer. And one of the primary benefits of Linux distros is that it essentially forces a moderator (the distro packager) between users and the upstream maintainer, who can step in and choose to side with the user or the maintainer (or neither!) if there's a contentious discussion. Again, taking Linux distros as an example, all the major distros have some form of appellate group of developers -- Debian's technical committee, Fedora's steering committee, etc. -- who are encouraged to moderate important and difficult discussions, and empowered to overrule package maintainers if it ever becomes necessary.
Preventing the repo owner from having the block tool wouldn't force them to come to an agreement with the contributor. They'd either keep yelling, use the (existing) close-and-lock-conversation button, ignore the contributor, or give up and get frustrated and burn out. I think it would be better to encourage social norms that allow handling these disagreements productively (and expecting that acrimonious disagreements will probably happen at some point,) than to expect to solve this by limiting technical tools.
By the way, note that blocking users is a feature that already exists for individual accounts. Extending it to organizations makes it ever-so-slightly easier for those norms to grow, by removing essentially the only disadvantage of maintaining your project in an organization instead of in your personal account.
