The side of the road is unsafe. Bikes should be following traffic laws, can't do that from the side of the road.

If there's a shoulder not covered in parked cars, of course they should be there. Safer for everyone. But in my small town most roads don't have a spot to ride, and riding on the sidewalks is illegal. So you go with traffic.

Now if you're lazing along at 6mph you're just impeding traffic, if you're that slow you should be walking. That's basically on purpose and I won't be defending that.