Musk is worrisome because after the innovation honeymoon is over, he could easily end up functioning as a closed-world promulgating autarch - just as Gates and Jobs did.
But Assange and Snowden? Their very popularity is founded on forcing open centralized amalgamations of power. They have localized power and surely an assortment of groupies etc, but these structures simply cannot scale to dominate a medium city, never mind the world.
So even if they are run-of-the-mill psychopaths playing their roles solely for self-advancement, the possible damage they can do is quite limited compared to say any unnamed multinational executive.
Capitalism created a Schelling point for getting useful public goods from self-interested parties. Compared to the prior most-lucrative path of government (likely via revolution), it raised the average amount of control for everyone while constraining the maximum control a winner could obtain. The general belief in free exchange of information advances this cooperation point to even smaller power structures, leaving the supernodes with even less privileged leverage over the rest of us.
Lots of evil is done in the name of "trying to make the world better". Its not unreasonable for people to be more interested in what they see your actions as likely to produce (and what they see that you reasonably should have known that they were likely to produce) than what you intended them to produce.
(And that's even before getting into the fact that "better" is subjective and one person's better can easily be another person's dystopian nightmare.)