When libertarians translate the idea of liberty into the political and economic spheres, they argue that government should operate only to protect personal liberty and not for any other cause. According to libertarians, the sole role of government is to enforce private contracts and to keep the peace so that no one can use force to deprive the liberty of another. In English political theory, this is called the "night watchman state."
By taking an extreme view -- that liberty alone is to be defended among all of society's values -- libertarians reach extreme conclusions. Suppose a rich man has a surfeit of food and a poor man living next door is starving to death. The libertarian says that the government has no moral right or political claim to tax the rich person in order to save the poor person. Perhaps the rich person should be generous and give charity to the neighbor, the libertarian might say (or might not), but there is nothing that the government should do. The moral value of saving the poor person's life simply does not register when compared with the liberty of the rich person.