If speed kills, then can you name precisely what speed... kills? If speed kills, as a matter of fact, it will be predictable and repeatable. It will be scientific. So, can you name that speed?
No... No, I don't think you can. That's because speed does not kill. Speed did not kill your friends in the car accidents you reference. Driving in an unsafe manner for the conditions is what killed them. Driving beyond the limits of their vehicle is what killed them. That can happen at any speed. Safe drivers need not to follow a speed limit to maintain safe driving habits. Safe drivers can drive at speeds that are comfortable for them, their abilities, and within the confines of the performance their vehicles are capable of.
If you're driving a high-end BMW, Porsche, Audi, Merc, etc. equipped with high performance tires, large brakes, and a large engine, and all the latest stability equipment... I challenge you to prove that driving an econo box at the speed limit is safer than the high-performance vehicle moving 30+mph faster.
You need to put speed in the right context. It's a condition. A factor. One of hundreds. In order to understand the big picture, and to properly assess risk, you need to combine that factor with not just mechanical factors, but also road conditions, and the human factor as well. An even greater risk to safety is driving with bald underinflated or overinflated tires, bad shock absorbers, sagging springs, tires rated underrated for the way you're pushing them, poorly maintained brakes, small brakes. These are the vehicles you should be most concerned with, because they're all around us. At ANY speed the drivers of these vehicles are dangerous. And they most certainly affect YOUR safety.
Now, combine a poorly maintained mini-van with the kinds of things a typical soccer mom does when she's got a car full of kids. She's doing her hair, she's putting on her makeup, she's talking on the phone, sipping her coffee, she's swatting the kids in the back seat, they're jumping around without seat belts on. Is she paying attention? No. Does she care about her safety? No. Is she attentive of the lane she's in, the drivers around her, and whether anyone is next to her when she changes lanes? Nope. Now imagine what happens when a vehicle like that exceeds the speed limit. This is what speed enforcement is designed to curtail. But what we're now witnessing is the widespread abuse of speed enforcement to impact safe drivers who drive above the speed limit in a manner that does not impact anyone's safety, merely for the purposes of revenue generation... under the thin veil of "safety".
Driving beyond the speed limit is not synonymous with reckless, unsafe driving. Unsafe driving is driving beyond the capabilities of yourself or your vehicle. What we need to be focusing on is lobbying law enforcement to engage in enforcement that is symbiotic with actual safety, and not merely a facade of safety that suits their revenue goals. Let's begin with lane courtesy, a law that's been on the books for a long time... and the system by which our multi-lane freeway system was designed. Once we get our heads in the right place regarding efficiency, reinforcing predictable driving habits of courteous drivers who are attentive and focused, we can then begin actually making serious progress towards a revolution in safe driving. Without educating drivers using public service announcements, and proper law enforcement, safe driving will be a fallacy.