A government exists to protect it's citizens. Any government that doesn't, doesn't deserve to exist. Let's look at the US government.
In 2004 crime in the US cost its victims almost 16 billion dollars. [cite(pdf, table 82)]
The criminals behind the current financial crisis have cost the US *trillions* of dollars. Clearly, theft, fraud, and all other property crimes are insignificant in the face of this disaster, and our government did nothing to stop it, and is holding no one accountable. They have utterly failed in their responsibility to protect us.
The WTC attacks on 9/11/01 killed nearly 3000 Americans and caused losses reaching 1.7 trillion dollars in the stock market. [cite]
In response, Bush went to war with Iraq. This war has killed over 4500 Americans and will cost over 3.5 trillion dollars. [cite(pdf, p.1)] Not only did the US government fail to protect us, they harmed us worse than Bin Laden did.
Let's keep going. In 2007, 775,138 people were arrested for marijuana possession. In contrast, 597,447 were arrested for *all violent crimes combined. [cite]. As you can see, the US government victimizes more of its citizens than it protects.
So what's left to justify the existence of this government? Majority rule perhaps? Well, Barack Obama got 62.98 million votes in 2008. The voting age population in 2008 was 230,117,876.[cite] That's 27% of our population that voted for this president. That can in no way be interpreted as a mandate to rule.
From all these facts and figures, one conclusion is clear. The US government has no claim to legitimacy whatsoever.