Cyclists are slower and plenty of cyclists will have had actual collisions or near-misses with eg car doors being suddenly opened into the bike line, cars cutting across the bike lane without looking, and so on.
Both riding a bicycle and driving a motorbike is less safe than driving a car because they are harder to notice and less protected but there should be some compromise between safety for a biker and noise pollution or a large are around the road.
As to cyclists to be slower: 1. a motorbike driver can choose to go below speed limit is the situation / road configuration makes it unsafe to go fast. 2. low speed is not always safer - on a straight road outside intersections speed of the flow (or just below) is safer.
As to cyclists to be slower: 1. a motorbike driver can choose to go below speed limit is the situation / road configuration makes it unsafe to go fast. 2. low speed is not always safer - on a straight road outside intersections speed of the flow (or just below) is safer.