That was in Atlanta where it is not legal. I also lived in San Diego for several years where it is legal and can tell you that these guys didn't do anything right. You do not split where gaps like that exist because you are still capable of making normal lane-change passes one by one. You do not ride at that speed differential because neither you nor the others can see each other soon enough to react. If you are passing between cars and there is a gap ahead on one side big enough for the car on the other side to change lanes into, you do not proceed. You match the speed of the cars you are between or fall back or move into that gap and prepare to move again if the car on the other side comes over.
It is more the lane-splitting rider's responsibility to watch for lane changes than the car's precisely because the car can't always see them coming. The rider has no excuse for going too fast to avoid putting him/herself between a lane-changer and an open lane. Motorcycles seat the rider higher than cars with much better visibility. Being between lanes also gives much better visibility ahead as well and the rider can spot gaps and react to cars in plenty of time as long as he/she is not going too fast. Regardless of how helpless the car driver feels when they see one zip by unexpectedly, they need to understand that it is as much or more the rider's responsibility to avoid YOU. Until you see it done properly from the rider's perspective (as opposed to from your car or these inflammatory YouTube incidents), it's very hard to understand that it can be done safely, but I assure you that it can.
I've had infinitely more cars obliviously change lanes into me while riding normally in my lane than I have lane-splitting because I am apparently invisible and I wouldn't lane-split where they would be changing lanes anyway. Period. Motorcycle riders are taught to ride like they are invisible because cars WILL make eye contact and then completely ignore you. It doesn't matter if they hit you illegally when you are dead, so it's still your responsibility to expect and react to it if you want to stay alive. Your nerves may be rattled when a bike you didn't see slips by responsibly, but be comforted by the thought that the rider saw you, assessed the it was safe, and was ready to react. He/she did not need your awareness to pull this off.
Now: go forth, and always use your blinker.
