Yes there are crazy cyclists out there. Once a year I meet one.

Do you know how many careless car drivers I meet? At least one each time I bike more than 3km. Not crazy (those I find every 100km), just careless. But thats enough to threaten my life.

Either way, the cyclist is on the receiving end of the risk (we're not talking about bike vs pedestrians here). So no Symmetry. Mass matters. A lot.

> Is it really important if it is 20 or 30 km/h? Is 20 km/h or 10 km/h not dangerous?

Yes, it is. At 10km/h it's really not dangerous; at 30km/h an open door may kill the cyclist, and a hitting pedestrian may be severely hurt them. Speed is that a relevant factor.