Hans-Hermann Hoppe defines the state:
What must an agent be able to do to qualify as a state? This agent must be able to insist that all conflicts among the inhabitants of a given territory be brought to him for ultimate decision-making or be subject to his final review. In particular, this agent must be able to insist that all conflicts involving himself be adjudicated by him or his agent. And implied in the power to exclude all others from acting as ultimate judge, as the second defining characteristic of a state, is the agent’s power to tax: to unilaterally determine the price that justice seekers must pay for his services.
Suppose you and your friends happen to be in control of such an extraordinary institution. What would you do to maintain your position (provided you didn’t have any moral scruples)? You would certainly use some of your tax-income to hire some thugs. First: to make peace among your subjects so that they stay productive and there is something to tax in the future. But more importantly, because you might need these thugs for your own protection should the people wake up from their dogmatic slumber and challenge you.
This will not do, however, in particular if you and your friends are a small minority in comparison to the number of subjects. For a minority cannot lastingly rule a majority solely by brute force. It must rule by opinion. The majority of the population must be brought to voluntarily accept your rule. This is not to say that the majority must agree with every one of your measures. Indeed, it may well believe that many of your policies are mistaken. However, it must believe in the legitimacy of the institution of the state as such, and hence, that even if a particular policy may be wrong, such mistake is an accident that one must tolerate in view of some greater good provided by the state.
Thus the reason democracy is evil.