By that token so is voiding your ballot, but if that were the only form of expression available to you, you might be happy to be able to make even that small squeak. Voiding your ballot (and in the same way, defacing a website) sends a message to your peers and the authorities that you are dissatisfied and that alone can be solidifying. That is one of the purposes of any protest, be it disassociating yourself from an injustice or creating graffiti to propagandize for your cause. It creates, at minimum, an opportunity for a group acknowledgement of that dissatisfaction. However imperfect the expression, it can still contribute to positive change. (I would also, for example, say self-immolation is a terrible waste, but it's damn hard to dismiss. In the same way, Aaron Swartz's death says something timeless, whether he intended it or not, and however regrettable or frustrating or futile or "selfish"...)

Is the sentiment of disapproval here due to one wrong being used against others (which I echo) or fear ("excuse for a crackdown")?