Your swinging a broad brush with the "no former military"

There are ex military more than properly trained and experienced to be a sheriff, State trooper whatever.
I did a hitch in the air force in the 80's, and had 2 jobs, IT guy and Security Police, (The security police side was so I had a combat war skill) Much of our training centered around when and how to engage a problem, and tons of practice.
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Security Police rules. - Protect the base and assets. IN some situations this meant deadly force authorized with little to no investigation. These areas were identified with LARGE 10' wide signs explaining you could be shot for entering the area and in certain rare instances the SP was required to fire.. IE weapons storage...
Law Enforcement Rules - Protect Personnel and enforce civil behavior on the installation. Basically same as a city cop.
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When protesters showed up it was Security NOT the Law enforcement side that engaged them. We had the training on how to engage them and there were like 400 of us and 40 law enforcement so they had us to spare.
We stayed on our side of the fence, if you crossed over,, it was abrupt, you'd be maced, hog tied and tossed in a van.
We had fire trucks standing by if a group got unruly and tried to cross in a bunch. A firetruck that can shoot water over 600 feet is a hell of a deterrent. Peels them off the fence like mayflies off a screen door with a super soaker (What can I say, off time in the military is boring in peacetime.... )
We didn't engage the protestors. No arguments etc. Heck sometimes we'd chat through the fence, because they were against nukes not us.. The locals knew the rules and behaved, it was always out-of-towners that ended up in the van.
You had to see the look on the face of someone sitting in the van, "I demand my phone call" - US,,, you'll get your call after the federal marshals take you off our hands until then we will lock you up and give you water.. Oh and it will be 24 hours or so till the marshals pick you up.
Like anything in law enforcement background matters.. I was courted by civilian law enforcement at the end of my hitch, by then I knew I didn't have the temperament to deal with people in that circumstance.