Deomocracy, in the sense of one person one vote for control over pooled resources, is inefficient because there is no way to communicate the intensity of one's preferences. That is one objection.
That is true, and it is one of the reasons why "democracy is the worst form of government there is". But other methods of reching "consensus" are not any better in that regard, often much worse; hence the other half of the saying.
While democracy does not
directly account for intensity of desire, it has some indirect ways. For example, if the majority chooses laws that are too unfair to some minority, the latter may resort to crime to make ends meet, or to terrorism and other anti-social behavior, in spite of the penal deterrents against such acts. Then the majority, if it is not too stupid, will usually ease the plight of that minority, enough to keep those reactions down to a tolerable level.
Democracy, like anything else, will function better if most of its citizens have more knowledge (especially of other societies, past and present) and more intelligence (especially the social intelligence I mentioned: awareness of the reactions that other people may have to one's own actions, and to the actions of the government. The fair treatment of minorities, above, is an example of decision that a majority will take if it has a minimum of those qualities.
That is one reason, by the way, why even the richest classes should want a good public universal education: because their welfare never depends only on their own qualities and actions, but always depends on the state of the society around them.
for example, if you don't have the right to take by force from your neighbor because you need his property more than he does, then you don't have that right even if the majority of voters decide that you do.
As I said in another post, "right" is a meaningless word if there is no government to decide who has it. Property is not a "natural right": you property is what your government thinks it is. There is no other useful way to define it.
You grow a crop on the land that is property of someone else: who owns the harvest? You may have signed a contract giving 90% of the harvest to the landowner, but if the alternative was to sign the contract or die of hunger, is that any different than him taking your harvest by force? You buy a stolen car without knowing that it was stolen; is it your property, or still the property of the victim? If you trace the history of a land plot back in time, you will almost always find that it was originally taken by force from the previous owner; so, is the present holder really the rightful owner?
In those and many other examples, there is no "natural" answer to the question. In each case, if the property right is disputed, the laws of the country will give general rules that say who has the property rights; a court would have to decide how to apply those laws to the specific case; and a government will have to forcibly enforce the court's decision, if the affected party refuses to accept it.
In the case where a country is at war the government can commander any private property it wants, and there's nothing the owner can do to stop it. The government can commandeer your house, your car, or the iron railings outside your house to make shells out of. The government decides whether you still own something when it's at war, and will use force to take it off you if you resist.