In the definition that says the ultimate source of government power is the people. You seem to agree that this is a reasonable definition of democracy. This means that they are a legitimate target when it comes to espionage or terrorism, yes. If you don't like it, move to a dictatorship.
They don't influence the government in its day to day operations, nor they have any special power or significance for the various policies as individuals (outside of their function as a voting majority).
So while this might make them a "legitimate" target for terrorism (in the sense: they voted for the government so they are ultimately responsible for its foreign policy etc) it doesn't make any sense at all regarding to espionage.