Everything hinges on what the guard can do. If he can shoot someone or put his knee on their neck, they’ll be effective. If all they can do is wag a finger and get hurt, well, they’ll be less effective. The Left has this teacher taking-control-of-first-grader’s view of how things will work. These aren’t small children and there is no extra authority given for wearing a uniform. In the case where no excessive force can be used, a uniform just makes you a more attractive target.
During the MLK riots in 1968, the Illinois National Guard put troops in the middle of the riot areas. They were assigned to stand under street corner lights with empty M-16’s and look tough. I would not expect much different today if the ILNG is deployed into the city.