It is dumb and nobody is 100% happy with it; but it does sort of work for the man in the street. I've got portable drives containing only work data, for example, that I have been "unfairly" taxed on because the copyright is 100% mine. On the other hand I have other drives full of films and music. So for me -a hybrid consumer/generator- it sort of works....definitely cheaper than buying CDs and DVDs and there's no chance of MPAA et al shenanigans (if I stick to private use and don't share them on the intertubes) or worry about the police kicking my front door in; which is nice and worth the money and being unfairly taxed periodically for me.
Most people are predominantly consumers, so it definitely works in that situation. Organisations that need large amounts of storage for their stuff aren't going to be thrilled; but I should imagine they'd treat the tax as an expense that they write off against other tax anyway; or simply buy their storage in another country that doesn't have the tax; or both.
Ironically, it's probably the rights-holders that are worst hit...in their greed to grandfather themselves a state-mandated income, they've effectively dropped a whole country-full of consumers off the map. And the small independents are even more hosed than usual. Amusingly, the rights-holders did try a "piracy is rampant in Spain" salvo; presumably as an opener to renegotiating but they basically got laughed out of the room.