There are no laws or ordinances against using sidewalks that I know of in Michigan. Possibly in Detroit but nowhere else that I can think of. Mostly I think commonsense should prevail. I use sidewalks mostly because they are there but sometimes if there is a lot of traffic on them I yield to pedestrians just as cars should yield (within reason) to me on the road.

I can see why some mid-size to larger cities would pass ordinances not allowing it because the pedestrian traffic would just be too heavy at practically all times to allow bikes on with walkers, etc.