What’s wrong with hiring a lawyer to assert your rights?
Safe harbor doesn't give much guidance to hosting companies about who needs to hire the lawyer, other than to note that if they try to practice law by adjudicating these cases themselves, they're on the hook to hire the lawyer.
The right approach in this case is not to waste money on a lawyer (or expect some lawyer to work pro Bono).
The right approach is to post about it publicly and bring shame upon GitHub for being the literal jar or of a Mr Steal Your Script. is
http://copyright.nova.edu/safe-harbor/
...and I think that if GitHub allowed them to post the content in the first place (ie it’s at the direction of the user, not GitHub’s moderators) and then when a red flag became known to them (for example via publicity) and they used common sense to ban that one repo, they would not lose their safe harbour they’d in fact be acting in accordance with it.
But like I say, I’m no lawyer.