Yes, spying to promote the interests of the people of the U.S. is legitimate in a world with other states with armies and the occasional bin Laden, etc. That's different from spying to promote the power of the executive, its fave corporations, the spies themselves, their counterparts in other nations, and who knows what else. The government is in theory our employees, and I feel more threatened by these employees who act like our masters than I do by their legitimate targets.

Assange's quote in the OP is all about alleged abuses that I as supposed employer would want to hear about: "Today we showed that UN Secretary General Ban KiMoon's private meetings over how to save the planet from climate change were bugged by a country intent on protecting its largest oil companies. We previously published Hillary Clinton orders that US diplomats were to steal the Secretary General's DNA. The US government has signed agreements with the UN that it will not engage in such conduct against the UN--let alone its Secretary General. It will be interesting to see the UN's reaction, because if the Secretary General can be targetted without consequence then everyone from world leader to street sweeper is at risk."