Decentralization is viewed by many libertarians as the best path to freedom, and there are none to speak of who would discount it entirely, even if they think it to be a secondary tactic to some other method. Thus far, decentralization has taken many forms. Bitcoin can grant its users freedom from taxation, currency debasement, and capital controls. Peer-to-peer file-sharing has limited the abilities of government to enforce intellectual property laws. 3D printers have the potential to render both gun control laws and patents irrelevant. Onion routing has freed many people from censorship and allowed for marketplaces that circumvent drug bans. These results are positive and growing with each passing day, despite the occasional minor setback.
All of these tools (and more) have been used to great effect to promote liberty by circumventing state power, but decentralization itself is fundamentally amoral. It is a tactic that can be used by the forces of darkness as well. The most prominent example as of this writing is Islamic terrorism.
There was a time when major terrorist attacks, like those of 9/11, were the biggest fear of people in the West. This was the height of centralized terrorism, when 19 agents of al-Qaida hijacked four airplanes and killed nearly 3,000 civilians in a well-planned, well-funded, highly coordinated operation. Here, the state displayed its strong suit: it can effectively destroy centralized enemies. If there is a physical target that can be bombed or a living person that can be exterminated, states are usually able to carry out those acts. (Of course, they frequently go overboard with their bombings and killings, which gives more people cause to become terrorists, but statists rarely care about this, as prolonged war is prolonged health of the state.) The regimes of the Taliban and Saddam Hussein quickly fell after the US military invaded their respective lands. But in their wake came decentralized enemies in the form of anti-occupation insurgents and new terrorist cells. These have proven difficult, if not impossible, to defeat. After all, governments, with their bureaucratic red tape and intrinsic inefficiencies, must be correct every time. Islamic jihadists, with their ability to remotely recruit and train new terrorists anywhere in the world, need only be correct once. They can even strike from beyond the grave, as videos made by the late Anwar al-Awlaki are still bringing new people into the ranks of Islamic terrorism.
So, what to do about the dark side of decentralization? It, like the darkness of centralization, is best fought with the light side of decentralization. We already have some examples of how this might work. After the Boston Marathon bombing, the city of Boston was put under martial law. But agents of the state did not find Dzhokhar Tsarnaev; a private citizen found Tsarnaev hiding in his boat. After the Charlie Hebdo shooting, 10,000 soldiers filled the streets of Paris. But they did not find the shooters; a man hiding under a sink in the building they occupied informed the authorities of their location. In both cases, locating terror suspects was better performed by private individuals than by government agents. The next step is to decentralize the means of dealing with the threat posed by terrorists by using competing private security forces against terrorists. This would increase effectiveness because private security forces would compete with each other to provide the best service at the lowest cost and could be fired for incompetence and/or overreach. And because aggression increases the cost of providing security, the sort of foreign policy misadventures that magnify the number of Islamic terrorists would be drastically curtailed, if not eliminated outright, if government militaries were replaced with private security forces.
Of course, central governments will not stop oppressing their populations unless and until they must, which will only happen with a combination of advancing technology and a willingness to use it in self-defense. In such oppression, centralization and the dark side of decentralization are allies, together for the long haul. For the state to win the war on terrorism would be against its rational self-interest, as the terrorists give the state an excuse to operate, grow, and oppress private individuals in the name of national security. For the state to lose the war on terrorism would also be against its rational self-interest, as failing at the one job it is supposedly solely capable of performing would quickly lead to its overthrow. The terrorists, for their part, need the state to motivate new recruits who would not be brought in by religious fundamentalism alone, as the military interventions that anger people in their home countries would be difficult, if not impossible, with competing private security forces in place of government militaries. In this sense, the state and Islamic terrorism are symbiotic enemies that must defeated together by the third side of libertarian decentralization.