The question seems to arise each time someone discusses the technique of lane "sharing" or lane "filtering". While the two are quite similar, there is a subtle difference between them. Lane "filtering" actually takes place not on freeways and open highways, but on city streets. Lane "filtering" is when a motorcyclist moves up between lanes of stopped or slow moving traffic to the intersection, and then proceeds on when the traffic control signal allows it.
Lane "sharing" is actually on highways and freeways. Again, only among slow moving or stopped traffic. Usually traffic flowing at speeds of 35 mph or less, and with a speed differential of no more than 10 mph above the speed of traffic flow. That 10 mph speed differential has two purposes, both safety related. The first purpose is to allow the motorcycle lane sharing to overtake vehicles safely and quickly. The second is to ensure a stable motorcycle speed to safely travel between the lanes of traffic.
A study done in Belgium in 2011 showed that if only 10% of commuters rode motorcycles and lane "shared" it would reduce congestion by up to 40%, and overall average commute times for all commuters by up to 20 minutes. Currently in Washington, we are hovering around 5% of commuters on motorcycles. Imagine how much traffic could be reduced if that 5% were allowed to lane "share" and not take up the same space on the highway as a car. Lower commute times would also correlate to lower emissions and a lower level of stress for all highway users.
In 2014 there were two studies done in California on the safety of lane sharing for the California Highway Patrol. A 2015 follow-up study all showed the same information. Motorcyclists who lane "shared" were shown to be; less likely to be involved in an accident, more likely to wear full safety gear, more experienced riders. The studies also showed that crashes among those lane "sharing" were much less frequent than other motorcyclists. The accidents that did occur; tended to be much less severe, with a greatly reduced risk of both serious and fatal injuries.
Now that you have the basics of the difference between lane "sharing" and lane "filtering" it should aid you in discussing the issue with your friends, acquaintances, and hopefully even your legislators. Perhaps you have noticed that I did not mention lane "splitting". That is because lane "splitting" is the same as lane "sharing" except at full highway speeds. Lane "splitting" tends to provide much less reaction time, and should only be performed by experienced riders. If the speed differential is still close to that 10 mph level, it can also be performed relatively safely.
Catch you on the road sometime...