Rather... a government has no 'duties' inherent except those necessitated by its being a government. For a being (or group of beings) to govern is for a being (or group of beings) to conduct the policy, actions, and affairs (of a state, organization, or people). And government is the name for the governing individual(s) or group(s). 
A government does not need to be also benevolent. It may protect the lives of its citizens... or they could matter so little to it that it kills them itself (Eg. http://en.wikipedia.org/wiki/Tiananmen_S...ts_of_1989 ). It may 'protect?' the 'liberty?' of its citizens... or the whole lot could be slaves to the government (serfdoms much?). A government certainly does not need to 'protect?' the prosperity of its people... else what of the poor?
A government does not need to be also benevolent. It may protect the lives of its citizens... or they could matter so little to it that it kills them itself (Eg. http://en.wikipedia.org/wiki/Tiananmen_S...ts_of_1989 ). It may 'protect?' the 'liberty?' of its citizens... or the whole lot could be slaves to the government (serfdoms much?). A government certainly does not need to 'protect?' the prosperity of its people... else what of the poor?
Please give me a home where cloud buffalo roam
Where the dear and the strangers can play
Where sometimes is heard a discouraging word
But the skies are not stormy all day
