The loosely organized hackers of Anonymous don't just launch distributed denial-of-service attacks for the lulz. They do it to send a message, which is why they've petitioned the Obama administration to recognize DDoS as a legal form of protest.
The petition, which was filed on the White House's We the People website, argues that DDoS "is not a form of hacking in any way" and that it's really not much different than repeatedly hitting the refresh button in your web browser, albeit on a much larger scale:
It is, in that way, no different than any "occupy" protest. Instead of a group of people standing outside a building to occupy the area, they are having their computer occupy a website to slow (or deny) service of that particular website for a short time.