Parents and People

There is no black and white answer to the question posed. Public opinion is important up to extent and should definitely be taken into account when forming state policies, after all a government cannot truly survive unless it has the support of its people. On the other hand there is the "parent" theory: children know what they want, but what they want is not always what is best for them. In such cases it is the parent's job to do what is best for their children - even if they wholeheartedly disagree.
Let's take apart the issue of state policy using this family metaphor. For example, we'll say that in the beginning of the summer Jimmy sustained a serious injury to his left leg and had to receive surgery. When the soccer season starts in September Jimmy wants to play on his school's team like he has always done, but his parents forbid him to do so - at least for the time being. Jimmy will naturally be very upset with his parents because he wants to play, and may even feel strong enough to do so however, his parents know that his leg isn't supposed to be fully healed for at least another month. If Jimmy's parents based their decisions only on Jimmy's opinion and let him play he could sustain further injuries which would not be in any one's best interest. This is not to say that Jimmy's parents should not take his opinion into account, on the contrary it is something that should definitely be considered. However they must also objectively weigh the situation and see which choice of action is truly the most beneficial.
There are also cases where the child's opinion should be the most important. Let's say that Jimmy's parents are trying to enroll him in ballet class. If Jimmy does not take ballet, his well being won't be hurt. On the contrary if he is forced to enroll in class (let's face it) he could be put under harsh ridicule by his peers. Because no ramifications will directly reach the parents regardless of what Jimmy chooses to do, yet Jimmy will be effected either way - the choice should strictly belong to him.
If we think of Jimmy as the public and his parent's as the state, what I am trying to say is basically that public opinion is not a firm basis for state policy, however the role that public opinion plays in state policy should be determined on an issue to issue basis. Other things, especially how each decision would effect the state and its citizens on the whole should definitely be taken into account. Citizens should have more input on issues that involve them more directly and less on international policies that will never effect them (this of course is excluding decisions to go to war and the like).