github went way above-and-beyond here. It is under no obligation to:

1) Enforce an invalid DMCA request

2) Take down forks and repos from other users, without DMCA requests

3) Threaten to ban users

DMCA has a simple, neutral process. github receives a request. It's required to take down that specific tool if it's a valid request (NOT everyone who forked it). The developer who owns that repo can then put that up. At that point, github brings that repo back, and gives the RIAA means to file litigate against the developer. It's inspired by the concept of a common carrier, where github would be acting as a neutral party, not a thuggish policeman-for-hire.

If github ignored DMCA requests, I wouldn't do business with them either. I expect them to be a neutral third party, as the law dictates.