The Github content is freely examinable.
Why not instead mandate access to the repos to an accredited external review authority that could flag the issues? Developers that really care about this could then sign up for it. Mandate a need to act on a takedown request, with an arbitration/review mechanism.
If dev X has issue Y against repo Z, that is much better decided externally and then notified to Github. There is no reason for Github to host "stolen" content, once that has been established, but asking each hosting provider to review stuff against potentially multiple jurisdictions' infringement criteria is silly.
Of course, having a member of the Pirate Party come out against this dumb directive makes it easier to dismiss criticism as the moochers' wish to continue unimpeded. But I don't think a lot of the honest contributors to Github, and I assume they are in the majority, would find any great amount of merit in this proposal as it stands.