Just incase you guys are also talking about cyclists, it's not that simple being in Toronto;
As a cyclist for the past 6 years, and also being in the industry, I deal with other cyclists all the time.
There are so many factors. Just the other day on queen street. Giant pothole in the side, and lots of cars on the road. What the fuck are you supposed to do? jump over the pothole? Sometimes you pretty much have to take the sidwalk.
There have also been countless times when I am riding on on a road with fast moving cars, and I have actually felt the car brush against my backpack. Sometimes they just don't give a fuck and practically hug you. It's such a scary feeling, Even as someone who has done this for years, my gut just sinks when that happens and I hop on the sidewalk for a minute or two. You actually feel as if you were about to die or get hurt badly. Now you can imagine how someone would feel if that happens, and them being a fairly new cyclist.
Not trying to make cyclists sound like angels and everyone else evil, but there are some good reasons why some folk ride on the sidewalk.
I also agree that some people are just jerks about it, and ride on sidwalks all the damn time, which pisses me off to; specially when they come up behind you and ring their bells so you move....I never move, because fuck you.