Similarly, a deer (which weighs less than a human on a bike and probably has a lower center of gravity) could never be a threat to a car. Running into a deer couldn't do more than scratch the paint on a car. I've never heard of a single person ever getting killed when they drove into a deer. /sarcasm
Bikes can certainly damage cars. I had a friend who went through a passenger window (breaking through the glass) of a car that pulled out in front of him. If that was the driver's side window, there is a nonzero chance that the driver might have been knocked out or somehow wrecked his car.
Also, cars (and their drivers) can definitely get hurt trying to avoid collisions with bikers by swerving out of the way and colliding with other vehicles/buildings/going off the road into a ditch.
The several grandfather post to this would have said essentially the same thing and would be much less controversial if it just read "a bike is less of a threat to a car than a car is to a bike", rather than using the absolutes of "always" and "never" (which rarely can be used to describe real life situations).
Also, despite historical claims, I'm fairly confident that most roads (by any reasonable definition of most) in the US today were built with the majority of design thought about drivers.