For those who don’t know, lane splitting is when motorcycles ride in the gaps between lanes of stopped or very slow cars in heavy traffic. It sounds intrinsically dangerous, yet is legal in California, and there is no abnormally high rate of crashes involving motorcycles there.
It should be legal everywhere not only because it enables motorcyclists to commute faster (thus rewarding people for using vehicles that burn less fuel), but because it enables better traffic flow for all vehicles.
Motorcycles, you see, can cause inefficient flow in heavy traffic. This is because motorcycles rely on the angular momentum of their wheels for stability, which in turn means motorcycles have a minimum speed, below which they become unrideable. When this happens, the motorcyclist is compelled to stop, which compels all following vehicles to stop. Slow traffic has now been turned into erratically-flowing, stop-and-go traffic.
Letting motorcyclists split lanes prevents them from being compelled to stop and mess up the traffic flow in these lanes. Thus it is a win for all road users.