You need some sort of hybrid approach, where you convince easiest 99% of people to be peaceful, but retain enough military capability to dissuade the remaining stubborn 1% from doing anything nuts. Which is more or less what we're doing today. Except some of those pursuing the hippie part of this hybrid approach have deluded themselves into thinking their approach will work on the entirety of the remaining 1% just because it worked on the first 99%.
That's what hippies don't seem to understand. Even if you temporarily achieved 100% indoctrination into a peaceful, cooperative society and completely disarmed. It just takes one person to be born who thinks differently and builds his own devices and following in secret, and spreads chaos and ruin upon that idyllic and disarmed utopia. You must have some sort of defense against this in reserve. Always. I don't particularly blame hippies for making this mistake - people tend to think that others will act as they themselves do. So if it's beyond their conception as to why someone would want to kill and destroy in order to have power over (parts of) the world, then it will literally be inconceivable to them that someone would ever want to do this. But that doesn't change the fact that it's a bad assumption.