I don't want to denigrate either of these two people; I wasn't there and I do not know what happened to cause the accident. A TV show speculated that the car was travelling at about 90 mph when it crashed based on a video.
I can say from experience that sometimes people think they are above danger and the laws of physics. People who should know better.
Years ago, around 1985, I attended the General Motors' Long Leads, a week long affair in and around Detroit. It was always near the 4th of July. Back then GM had Buick, Cadillac, Chevrolet, GMC, Pontiac, and Oldsmobile and there were five full days of the upcoming models. That year Cadillac was the official "car" of the Michigan Indy Car race. I remember we had lunch at some swanky country club (I chatted with Rick Mears who was still suffering pain from a terrible accident in testing - he kept shifting his weight from one foot to the other), and after lunch we went off to Michigan International Raceway to drive the "new" Cadillacs around an unused road course. Some of the journalists were driven to the track in cars driven by some of the race drivers.
Evidently a couple of drivers who shall remain anonymous (one was a junior, the other had a terrible accident hitting the outer pit wall at Indy) got a little over competitive and raced all the way there; both with a car load of journalists. On public roads. Good fun.
You don't normally think race drivers would be that crazy on the street. On the track, at least in theory, they are surrounded with other professionals. But on the street who knows who is beside them?
I've seen far too many supposedly sane people, knowledgeable drivers, drivers with above average skills, act like fools on public roads. I've done it myself. I like to think I've matured.
So my thought is that Roger Rodas, a race driver who was driving the Porsche that Paul Walker was a passenger in should have known better. Public roads are not race courses. Hazards are unexpected. Who knows what happened to cause the Porsche to go off the road. I read that someone speculated that Rodas may have hit a patch of sand, oil or water. Or maybe a animal darted out. We will probably never know.
What I do know is that both Rodas and Walker should have known better. The Porsche Carrera GT has 558 hp, will do 0-62 mph in less than 4 seconds, and has a top speed of over 205 mph. It is essentially a race car for the street. It should have been able to handle the corner at the estimated speed - If all the conditions were perfect. Perfect is not a term that applies to public roads.
It is tragic that two young men with promising careers have been killed. It is lucky that no innocents were taken. Life is not a movie where cars crash and people walk away.
When James Dean died there was a saying, one that was falsely attributed to him (it came from a book  and movie , "Knock On Any Door"), "live fast, die young and have a good-looking corpse." There are no good-looking corpses, only dead ones. There is nothing romantic about dying in a horrible accident. Leave the racing for the track.