Since people have disparate preferences, interests, and ideas about the world, it is unlikely if not impossible for a government to exist where everything is unanimous. People can even disagree on legislation because they think it goes too far or not far enough. In American politics, for example, after the Pearl Harbor Attack, the vote in congress to declare war on Japan was not unanimous.
One fictional example of what you are describing is the unification government type in the PC game Masters of Orion 2, but this relies on non-human aliens being fundamentally different from humans.
Milton Friedman's idea of "unanimity without conformity" is related to this idea. Friedman's idea is that, in a market, all parties to a transaction must unanimously consent. If I want to trade you $3000 for your old car, we have to unanimously agree that we are both better off by this transaction. In contrast, a government decision that everyone must own a specific car, would force people who don't want that car to own it. It would force conformity(everyone being the same) without unanimity(everyone agreeing to the change). Friedman uses this idea to emphasize that market transaction which are unanimous are generally preferable to government mandates, which force the will of the majority onto minorities. Obviously, externalities mess this up, but that's a different topic.