I believe there's a legal difference between overtaking and filtering. Whilst overtaking is an entirely at-risk move, I don't believe filtering is.
I'd consider filtering much more dangerous than overtaking. If you're simply overtaking it's only a few cars at a time - quick twist of the throttle and most bikes will blast past a row of cars in a couple of seconds.
Filtering is a continuous act. It's not over in a couple of seconds and you need to take constant care to avoid turning cars, cars changing lanes, people too close to the lines (on both sides of the road), oncoming traffic etc.
I've been riding bikes since I was 16 and will, usually, be the first to defend my fellow biker but in cases like this I really do wonder why the car driver is entirely at fault.