Come out against the RIAA if you must do something. Better still to let the process work, you don't win legal battles by committing crimes.
It's unreasonable to expect that the individual who took this action could go to court against the RIAA and extract their deeply embedded claws from the legislative, executive, and even cultural environment in which they've entrenched themselves.
Instead, it's reasonable to expect that somewhere in a conference room at say, Gitlab, Sourceforge, etc., sometime in the near future, some lawyer is going to mention "We got DCMAs from X for repo Y, and foo for repo bar, and from the MPAA for the popular repo (insert software tool here), obviously we should remove all of those repos." Maybe someone familiar looks up and says "that sounds a little silly, isn't that tool just a general-purpose media player?" And the lawyer might respond "We don't care-we don't have the budget to determine if the DCMA notice looks valid or not, if it turns out to be valid we have to do it and if it's not valid it costs us nothing to take it down". Actions like this provides a reasonable response of "But, as we saw with GitHub, some of our users and maybe even some of our own employees will resent us for this. It could cost us users, cost us bad publicity, or cost us real money. Let's put a couple people on this for an hour or two to estimate the pros and cons."
Github was just a middleman, responding rationally to their existing financial, legal, and moral incentives, in a battle between their little users and the RIAA. Like a little flock of oxpecker birds riding a rhinoceros, we wouldn't even register in a fight against a tiger, we can only warn our larger intermediary of the danger we perceive. The RIAA doesn't care that you're against them. We need to change the incentives for companies like Github that have a chance to be heard.
That being said, it also seems like GitHub is well within their rights to choose not to host a project accused of violating the law.
Tell that to the Civil Rights movement.
GitHub (via their owners Microsoft) is a member of the RIAA. They give the RIAA money to do stuff like this.
Quite possibly one of the most incorrect things I've ever read.