IT'S ILLEGAL - The law in most areas of the country require bicycles to follow the same rules of the road as other motor vehicles. In essence, riding your bike down the sidewalk is the same as if you hopped the curb and started rolling it in your car. IT'S DANGEROUS – Riding the sidewalk has it’s own set of dangers that many people never think about. Getting right hooked, cars pulling out of driveways, hitting pedestrians, etc are all things that have to be carefully watched for.
Thanks for the wonderful copypasta, Nonny, but see my previous ask answer, please.