I think it's simplistic to call a democratic government a "gang", but even within the analogy, the danger of having zero is that the resulting power vacuum isn't a stable system. Gangs will spontaneously arise as people who have the talent and skill to lead men in organized violence realize that doing so is the rational course of action in a world with no higher power to stop them.
Interestingly, all the Bitcoin heists are great examples of this. What are they other than (digital) violence? I think they clearly demonstrate that when people are unrestrained by some power, that many people will realize it is advantageous to take rather than to transact in mutual ways. Now, I'm willing to entertain the idea that there are solutions to this problem that don't involve centralized power, but I disagree with libertarians who throw around the word "violence" as if it's some creation of government rather than something intrinsic to and widespread within society. It's not something that can be taken off the table with a declaration, but a problem that must be managed through some mechanism.