Then the car serves as the immediately threat to the other car, no the cyclist. This why you are supposed to drive defensively when operating a motor vehicle, so sudden changes in a situation doesn't cause you to crash into someone or something.

When you're behind the wheel of a car, yes. When you're around a car, no.

Even if someone's driving defensively, sudden changes in the environment lead to a more dangerous situation. If they're driving defensively, hopefully they can deal with it, but that is no reason to create dangerous situations in the first place.

...both car's passengers are surrounded by a metal cage that is trying to protect lives.

Are you being deliberately daft? Yes, the people in the cars are safer than a reckless person on a bicycle, but that doesn't mean the bicyclist isn't still putting them in some danger - those metal cages don't always succeed - as well as putting pedestrians and other bicyclists in more significant danger.

Okay, a reckless cyclist can put a driver in some danger, if the driver is going fast enough that the car can't be stopped quickly enough to avoid either hitting the cyclist or swerving into an oncoming lane.

However, in this constructed situation, it seems to me that the driver is being more unsafe by driving that fast.

So, you're in favor of lowering the speed limit to like 15 mph?

Yes: http://www.20splentyforus.org.uk/

If that's the parent's position, then I'm not sure I agree but I can't fault them for inconsistency. In an environment where many cars are traveling faster, though, it is nonetheless irresponsible and dangerous to others to ride a bike recklessly (or otherwise be unpredictable near fast-moving traffic).

I will agree that a relatively slow-moving bicycle on a road with fast-moving cars is indeed a dangerous situation for everyone. And I would agree that having similar speed vehicles together seems safer.

However, in places with vehicles going differing speeds, I would put the onus of safety on the faster vehicles.

What was being discussed was cyclists behaving recklessly. Imagine a cyclist blowing through a red light at the bottom of a hill, where they're going ~20ish. Cross traffic with a green light isn't necessarily going to see them until the last minute even if the cross traffic is moving at an otherwise safe speed. Pay attention in a city for a while, and you'll see things like this, and it rightly pisses off both drivers and us other cyclists.

I thought we were talking about whether or not bikes can be a massive threat to cars.

I have been paying attention in a city for a while. I have seen the situation you describe, but it's rare in my experience, even with SF supposedly full of reckless fixie-riders. Dangerous driving is far more common in my experience.

Hmm, yeah, scrolling up, there was more than a little hyperbole on both sides at the root of this thread. I agree a bike is not a "a massive threat to a car"; this doesn't mean it's okay for people to ride recklessly, or that they're not endangering others when they do.

And dangerous driving is probably more common (certainly by number of instances), and it should be condemned as well.

I certainly agree with all of that.

Stop being obtuse.

I wonder if someone could find stats on how many car-on-car collisions are caused by avoiding a bicycle, and compare that to how many car-on-bicycle collisions are caused by a swerving bicyclist (or any cause, really).

And then look at the resulting injuries.

No one is disputing that a reckless bicyclist is a danger to themselves. The question is how much of a danger they are to others, because more people feel more okay intervening when someone is presenting a danger to others.