I've Made a Video about Anarchism

[Anomalocaris]

How does a community militia stamp out its own power grab?

Anything that can stamp out a power grab can grab power.

Why would you automatically assume that any and all power grabs would come from a militia, when presumably virtually everyone in society would be armed? 
Seems to me that militia members wouldn't be any more inclined to long for a reestablishment of strict governance than any other group of yahoos--perhaps even less likely. Actually, I would think that militia members would be more likely to value the core principles of anarchy and value "Muh freedom!" more than anyone else.

The whole Everyone being armed, second-amendment-being-protection-against-organized-tyranny is fundamentally laughable.   An armed but relatively untrained and unorganized mob tends to self-eliminate through klutzy fratricide if its arms are called upon.    An organized and even partially trained armed organization would be a match for an unorganized and untrained armed mob many times its own size.

So in the anarchic world, a thinking person with a mind for power grab will focus on creating or coopting the only organized armed body in its community.