My take on this touchy subject is simply my opinion based on better than a half century as a licensed motorcyclist.
Lane-splitting is a great idea in theory, but rather problematic as to its practice. Why so, you might ask?
Simply stated and an oft-repeated caveat throughout this thread is that it's all good "if done safely" and the reiteration of requirements that lane-splitting or filtering necessitate excellent and consistent applied discretionary skills and decision-making on the part of both types of vehicle operators involved - i.e., motorcyclists and the other motor vehicle operators sharing the same road must all be alert to conditions when it will likely occur, aware that the practice may occur at any time (and speed), that they should be equally considerate of one another's rights of way and that both parties must exercise good judgement, proper safety technique and appropriate courtesies throughout the mix of conditions and circumstances where and when lane-splitting may take place.
Those are a lot of conditions and expectations that should be both operative and prevalent should there ever be a possibility for lane-splitting to occur regularly and with minimum negative incidents on any public roadway.
Now, I have known, throughout the long span of time that I've been a licensed motorcyclist, that I will exercise all of those necessary caveats I delineated above whenever (well, at least 98% of the time) I even considered lane-splitting myself. That said, I can't count the number of times over the decades I've been driving or riding that I have been taken off-guard by someone splitting lanes unsafely, insanely, at ludicrous speeds or in totally inappropriate situations, such as at posted highway speeds or above and by idiots utilizing the practice on a roadway or highway's shoulder or when traffic is at or virtually at a standstill and the practitioners whiz by between lanes or on the shoulder of a roadway at terrifically unsafe speeds. More than once I've nearly stained my manties or suffered an elevated heartrate or a form of passive, unacted upon, road rage.
Even as a lifelong motorcyclist, I often wish that I could suddenly open a door or have a hood-mounted Barrett rifle to cull the dipchits risking their lives and the lives or property of others from the herd. On the other hand, given the general dereliction of responsibility, ignorance of the law or near total lack of basic driving skills or common courtesy of what I perceiveto be the majority of motorists on the roadways, cagers and other non-two-wheeled operators are not only no better a risk than the idiots I often see on motorcycles, they are very measurably the greater risk to we who enjoy two-wheeled transport when it comes down to making the decision whether to lane-split or not.
There is a lot of trust involved in this issue. Trust that the motorcyclist chooses his spots carefully and then exercises the maneuver safely and trust that all others on the road with us will also utilize vigilance and awareness of the practice as well as applying good judgement and courtesy with respect to we who are at infinitely greater risk of critical or mortal injury should a mistake be made.
Although I take the inherent position of the OP, Captain Smith, at the end of the day, the sort of trust involved for this practice to go well often amounts to blind faith on the part of the motorcyclist and, consequently, I exercise my legal right to lane-split very, very judiciously because trusting the others on the road with us is a long-term bad bet for folks on motorcycles. The more frequently and longer periods of time you bet on the other guy doing the right thing, the greater becomes the probability of their doing exactly the opposite of what we expect them to do or how we assume they will behave.
I'd much prefer to see a portion of wider roadway's shoulders (on Interstates and major highways) dedicated to two-wheeled traffic, but only when the roads are congested and average speeds on the main roadways are 25-30 mph or lower. That could be tricky, as well, but I think it could be safer for us overall.