A government by definition is a monopoly on violence, which leads to the next question - why would any goods or service require a monopoly on violence?

I would argue a coercive monopoly on any market is counter-productive and unnecessary (they even claim to protect us from such monopolies, thanks SEC). Even if we're talking about delivering mail, UPS, FedEx and DHL are evidence that an involuntary service CAN be provided voluntarily. Voluntary is always better than involuntary.

Does laying tar on the ground need a monopoly on violence? What about delivering packages? Collecting taxes actually DOES require such monopoly. Markets work because humans have preference. Even a democratic government cannot account for the preference of it's territory without disenfranchising a large population! If you don't like blockbuster, you can use netflix. Don't like UPS? Use fedex. Don't like Homeland Security? Well that's too damn bad.