Training isn't the issue, it's the lack of accountability. Military members are under the threat of being court martialed and spending time in military prison. They know they have less rights in military court than they would as civilians, and that punishment can be harsh.

Cops, on the other hand, know that the system will bend over backwards to accommodate whatever transgression or crime they commit. They can and do act with impunity, because they're actively aware of that impunity. They know that if they get caught, in the worst case scenario, they'll get a paid vacation, their boss will allow them to resign, and they'll have to work one town over.