I don't think that would be a good idea either:

"...sending a takedown notice, if you are not the copyright holder, is what's actually against the law."

As noted in other comments, this notice does not even mention copyright, so that law is irrelevant.

A cease and desist letter is not a DMCA takedown notice.

The discourse so far has been pretty polite, aside from that last crack about "lifting" the content. It would be fun to send it back, but the reasonable response is just to reiterate the previous points about there being no copyright holder, and they will be happy to comply once there's some legally binding reason to do so.

Which is never, thanks to fair use.