A bill introduced in Maryland last week would make sidewalk cycling legal everywhere except where explicitly banned by law. Currently it is illegal unless explicitly allowed - as is true in Montgomery County. I think this is a much better approach since, on average, I think cyclists are better off with the option. In most cases cyclists will choose the road, but there are a few places where sidewalks might be preferred (I get on the sidewalk to go up two foreboding hills on my commute every day) and it would be hard to determine and legislate each of those one by one.
I know some cyclists are opposed to sidewalk cycling at all times, but I'm not among them.
One of the sponsors of the bill, Aruna Miller, is a Montgomery County planning and traffic engineer, so it's nice to have someone pushing the bill who can speak with some authority.