It is illegal to distribute a "device"(very broad definition) that can circumvent DRM. The protest is against how broad and vague that prohibition is and that

It is illegal to distribute a "device"(very broad definition) that can circumvent DRM. The protest is against how broad and vague that prohibition is and that it prohibits items even if their normal/much more useful function has nothing to do with DRM. Such as prime numbers or Sharpie markers. A "Hey legislators, in your scramble to sell out to content industry you've just made these numbers illegal." kind of thing.