Not all hackers are activists.
Even some ‘members’ of the notorious online vigilante group Anonymous do not act in the best interests of the public. Hacking in the hands of the right people ( and thats the question, who are the right people? ) has the potential to be a great tool for championing, informing, protecting and educating the public. Hacktivism as well as the information that is released can be misdirected and become a tool for misinformation.
One thing to keep in mind though when considering Anonymous is that they are as you state decentralised. Due to this any individual can claim to be a part of Anonymous. This post on a forum site surmises this notion quite well “it is nothing more than a name that different groups can hide behind in order to leak/drop information and attach itself to the Anonymous “brand”
Whistleblowers like Snowden and Assange do educate and inform the public, but what happens to the information after they release it? People will continue to believe what they wish despite the new evidence. Take for example the ‘fappening’ or as it should be known celebrity nude leaks scandal a case of hacking where individuals are targeted and exploited. Assange and Wikileaks on the other hand use hacking to promote activism and a culture of scrutiny focused on large corporations and governments.
Hacktivism is a great tool for promoting transparency in governments and corporations, I can only hope that it continues to be used for good.