The main problem with ancap is that there's nothing preventing a violent gang (a new government if you will) from forming, because everyone else is being so peaceful, and if everyone else stops being peaceful, then it it isn't ancap any more - its just regular anarchy.
Ancap will only work if there is some force to stop people from conducting acts of violence, preferably some force that isn't corruptible. So, until we have open-source peacemaking enforcement droids no such utopia can exist.
That was the case many years ago when the nobility had castles, horses, swords and so forth and the peasants had pitchforks and sack cloths. And true to a degree currently where the government gets the most fun toys. But in a modern society, the people would have access to the same kinds of weapons as your gangs and the gangs would have a much harder time establishing any kind of footing. It's no accident that the American revolution occurred at a time when important changes in personal armaments were happening.
And after all, it's not like places with governments are exactly gang-free either. Especially where the citizenry are disarmed.