There's nothing wrong with riding on the sidewalk as long as you're careful and it's not crowded. You shouldn't go blasting down it, but if it's safe and legal, what's the problem?

Sometimes it's the only sane option. While I can legally ride my bicycle on a four-lane road with a speed limit of 45MPH and no real shoulder, I'd have to be crazy to prefer that to the sidewalk that sees perhaps one pedestrian an hour.