Democracy is the rule of the people. The most prevalent form of democracy used today is representative government; people elect their representatives and these representatives run the government. You would think if people have a choice on who runs the government, their freedoms will not be curtailed. This is extremely incorrect.
Democracy is useful from one perspective -- stability. If majority of people have selected a government to power, chances are slim that the majority of people would be unhappy with the government. They would surely not be unhappy enough to lead an uprising. This means a democractic government would mostly lead to clean and smooth transfers of power.
This can also mean that in a democracy, the majority can make rules and regulation which are not popular with the minority. There is no issue with stability, after all the minority cannot have an impact on the government.
You would think surely this cannot be happening -- the majority would look out for the well being of the minority. After all, the usual rule is "do not do onto others what others would not do onto you". Well, it depends on whether the majority thinks the minority is "at fault". I would suggest you to look at the tax code. Rich people pay more tax than poor because they are in minority. The usual argument is rich people have so much more money, so they can surely afford to give more, but nevertheless, rich people have lesser freedom with their property than poor people. This works OK since even if all rich people decide to vote the government out of power, they wouldn't have enough votes. A lot of populist protectionist measures get passed on account of the majority thinking the minority is at fault.
Another way in which the majority can decide to curtail freedom is when it thinks the whole population is at fault and it is its duty to fix it. As example, take "global warming" or "mortgage crisis". Regulations are made to fix the energy industry or the banking industry because something they did or are doing has supposedly caused problems to all people. These regulations however would apply to everyone equally -- if I decide to open a bank now, I would have more regulations than 2 years ago.
Is it really necessary to curtail freedoms of people? Surely, there can be no valid reason to reduce freedom of some people as compared to others. There is also no valid reason to reduce freedom of all people to say fix "mortgage crisis". If there is a problem, spread the word about causes and consequences and majority of people will adjust their behavior automatically. This means that the crisis would go away.
