POLICE chiefs controlling military equipment and using military tactics is a recipe for disaster.
True, but not for the reasons you are implying. Most police departments barely can afford enough officers to patrol the streets and chase down the criminals. Putting together a military unit for an arbitrary purpose would be beyond the reach of nearly all departments. Trying to restrict freedoms in any meaningful way would be near impossible without an overwhelming voluntary compliance.
The difference between John Q. Public and his .45 vs. Jimmy Q Police Chief and his MRAP, is that the founders tried to write the Constitution so as to insure Mr. Public the freedom from Mr. Police Chief acting as a military unit and taking his freedoms away.
Even if they could the effectiveness of acting as a military unit would be horrible. They simply don't have the resources (man power, logistics, infrastructure), training or skill set to operate as a military unit. They don't have any means to acquire these things either.
I'd much rather see these vehicles offered to rural fire and ambulance services.
The off road capability of an MRAP leaves much to be desired.