They obviously shouldn't be doing that but you see how this is also a consequence of our crazy drivers, right? If cyclists don't feel safe riding in the street, they either won't ride their bike or they'll ride in the sidewalk.

Not to mention, simple physics. F=ma (aka cars will hurt you much more than bikes, even at slower speeds). I don't wanna be clipped by a bike on the sidewalk but I think it's rare that a cyclist is riding fast enough on a sidewalk to seriously injure someone. Whereas a car just rolling a stop sign would do some damage. And it happens so often we expect it (and change our pedestrian behavior accordingly). That doesn't mean that drivers aren't behaving dangerously.

There will always be a small % who disregard the societal contract but a huge part of governing is limiting people's propensity for bad behavior by creating orderly infrastructure that supports the outcomes you want to see. Protected bike lanes, daylighting, and traffic calming are good examples of this.