Duh! In most European countries, you have to prove you can competently "filter" (aka lane split) in order to get a motorcycle license.
The ability to keep moving when cars are stuck in stop-and-go traffic is the killer app for motorcycles and motorcycle sales. And the motorcycle lobby (as fractured as it is) has finally done a decent job of convincing legislators across the U.S. that it can be done "safely". The challenge is that a significant number of drivers (read: most voters) are still against it.
When surveyed, uninformed drivers cite "danger" as the reason they're opposed. They also claim they're frequently startled by motorcycle traveling between lanes (solution: pay attention) and, less frequently, claim it's unfair that motorcycles can get through stalled traffic when cars can't.
In my work in the ad industry, I've organized many consumer surveys, and I can tell you that even anonymous respondents tell interviewers what they think is the best answer, not necessarily what they really feel.
The primary opposition to lane splitting is that rarely-mentioned issue of fairness, or its corollary, cage-drivers' territoriality. So if the people lobbying for lane splitting want laws to pass, the argument they need to make is, allowing motorcycles to filter helps everyone get to where they're going faster.
Every vehicle that moves out of the traffic column (and into the interstitial space between lanes) speeds the flow of the column, not just the flow of motorcycles. And traffic engineers can prove that sometimes even changing the number of cars/hour by a few percent can make the difference between flowing and stop-and-go traffic patterns. By allowing lane splitting, legislators will
- improve traffic flows for cars, as well as motorcycles
- improve the economy and sales tax revenues by encouraging motorcycle sales
- increase the number of commuters who choose motorcycles
- free up parking spaces
- reduce the production of CO2 and hence, reduce global warming
To recap: the way you get lane splitting laws passed is, by making it clear that lane splitting will improve traffic and parking congestion for cars.
As for safety, you can easily protect motorcyclists in the long term by writing a proviso into laws that lane spitting is only legal when motorcyclists wear helmets, and by specifying that if states with mandatory helmet laws repeal those laws, that the right to lane split is automatically also repealed.