I've lived in the Bay Area all my life, so I've seen this practice plenty of times. While I've never personally witnessed an accident, I've seen a number of close calls.
Flux, a lot of what you are talking about with people "doing it right" is good in
theory. But in practice, it's another matter.
I am on the Bay Bridge during rush hour every weekday, and have been for the last several years now. Being on a bus (and being someone who sometimes passes the commute by making sure I snag a seat that will afford me a good view and then just traffic+scenery watching the whole way), I have a good vantage point. I can see the entire roadway and all five lanes very well, and one of my problems with lane-splitting is that cyclists do it ALL THE TIME. The only time they don't is if traffic on the bridge is moving at a steady 50 MPH (which, during rush hour on a weekday, is rather uncommon). If it's anything below 35-ish, in comes the splitting.
I can kind of see an argument for motorcycles being allowed to do this in STOPPED traffic, or traffic that is moving at like... 10 MPH (with the cyclist allowed to go maybe 20, tops). And I don't even have too much of a problem with the base concept, in and of itself, that a motorcycle could be afforded some extra privileges on the road simply because it's smaller and more fuel-efficient. After all, that's why they can use the HOV lanes despite being one-person vehicles. At the other end of the spectrum, all accommodations for buses on roads and highways (of which there aren't nearly
enough if you ask me, but there are some, such as a bus and taxi only lane leading up to the Bay Bridge in SF that AC Transit's transbay buses use) are based on the same concept. This is a vehicle that transports many more passengers than any auto could possibly hold, so we reward the people that ride it by allowing their vehicle to use HOV lines and blocking off some parts of the roadways as bus only.
My problem is that if traffic is moving, steadily, at 20 MPH or above, then it becomes completely unnecessary. That's plenty fast enough for a commute/rush hour situation. No, it's not
ideal, and no, it's not the speed limit on the bridge, but it's just not a big deal. If traffic is moving at 25 MPH, just stay in the flow and go at the same speed as everyone else. Motorcycles routinely split at such speeds, and I also often see them diving in and out of the traffic flow repeatedly and cutting across lanes. This strikes me as extremely unsafe, and at that point, you're just being greedy. There is no good reason why motorcycle riders need to be given this accommodation to engage in highly dangerous behavior to avoid the horrendous fate of being stuck in 25 MPH traffic for an extra ten minutes.
I also have to agree with others who question the logic of the "I'm helping out by getting out of the way" defense. Motorcycles are too small and too few in number for that to really be significantly beneficial. I'm firmly of the opinion that lane-splitting benefits exactly ONE class of vehicle on the road: the motorcycles themselves.
For everyone else, it just makes things more difficult. In particular, a couple of things from
Hocutus:
What if a car has to swerve a bit to avoid an obstacle in the road or another driver encroaching on their lane because the car is in their blind spot and they try and change lanes? Now they have to worry about motorcycles being in the gap that would normally have been some free space to safely maneuver.
This strikes me as a major concern, and is the issue in the majority of close calls I have seen. Car drivers have enough to worry about as it is (and not all drivers are paying enough
attention to all that stuff as it is); they don't need to have this in the mix, as well. Lanes were not designed to accommodate a vehicle in between them like this. Just because it
can be done doesn't mean it works
well. The space being occupied by the motorcycle is SUPPOSED to be a fallback space for emergencies, sudden unexpected movements by other cars, etc.
While it's good that it makes it more obvious that you're coming, having a huge noise from a bike suddenly blow past you can also be distracting to the driver (not to mention a major irritant).
On this, I've been in a car (as a passenger) when motorcycles have passed by me. It can be quite jarring, and definitely can be a distraction to the driver.
Contrasting motorcycles and buses again, a bus-only lane across the bridge itself (i.e. the whole way, not just the on-ramp) would make a LOT more sense from this perspective, because moving all the buses out of the flow of traffic would actually have a major impact on said flow and the ease with which cars (and bikes) navigate it, because buses are HUGE. So it would not only benefit the bus riders, but actually would benefit everyone else, and isn't potentially very unsafe like lane-splitting is.
Again, a proposal to make lane splitting legal ONLY when the traffic is moving at something like 15 MPH or less, I might be able to get behind. Even then I'm not 100% sure about it, because as has also been pointed out, there are still hazards at those speeds (or even in completely stopped traffic), and I'm not sure it's worth it. But anything above that? No. The way things are now? No.