I have seen some interesting psychological commentary about the effect on crowds of being policed by faceless armored automatons versus guys in regular uniforms. The idea being it encourages more anger and violence. I'm not sure whether I buy that or not.
I'm not as worried about the equipment as I am the attitude and tactics. You can violate someone's civil rights just as effectively with a revolver, a nightstick, and a water hose as you can with an M4, taser, and armored vehicles. The problem is the apparent willingness by many police departments to do anything to ensure officer safety and catch the bad guy. No matter what the consequences are or what civil liberties are infringed. Which results in things like no-knock raids for non-violent crimes, violating a guy's rectum because the cops thought he might have drugs up there, the tendency to immediately go for a gun over a less lethal option, and all the other bad behavior we've seen lately.
Reducing the military surplus program might help change the attitude of many police. But I think the root problem is not the equipment, but the attitude. Anymore than the root problem with a school shooter is the AR-15 rather than their own mental issues.