On a tourist day (which is most of the days and most of the videos...) there are only two requirements to be on the Ring. You must have $20, and you must have a vehicle that moves. Expectations from PCA events are that the cars all have tech inspections, the drivers are vetted by run group for safety and ability, and that everyone is sober. This is NOT the case on tourist days. While as Misha said, traffic law dictates that the Ring is a toll road with standard road rules: " stay right except to pass" - do you want to have carved on your tombstone: "...but I had the right of way!"?
How you drive depends on a lot of things. Two big factors are "how rich are you?" and "how much life experience do you have (age)?". If you are 25 years old and inherited a billion-dollar trust fund when you were 18, you are both immortal and invulnerable (due to age and experience), and do not give a shit if you wreck your car (because you can just buy another one). Since I am old and not rich, I pass very carefully at the Ring. In particular, if someone signals as you are approaching, the most important message I get from that is "I see you". If they already have a signal on when they come into sight, they probably just forgot and left it on. If they never signal, it probably means they do not know you are there, they plan to use the whole track, and/or that they are inexperienced and dangerous.
Misha indicated that by law, either the BMW driver was at fault, or it was shared responsibility. While I would argue that it is shared responsibility, I think that the GT3 driver had more ability to prevent the crash. The BMW driver clearly did not see the GT3 (or would not have cut him off). The GT3 driver had NO indication that he had been seen, so as an experienced Ring driver, he should have expected the BMW to use the whole track (IMHO).
If you have done track days where you had a formula car in your run group, you know how aware you must be to share the track with a car going twice your speed that is only two feet high. In the longest video I saw, it looked like the GT3 was only in the BMW's mirror for 10-15 seconds, and closed very quickly. If the BMW driver's attention was all forward, trying to figure out where the track went around the next curve, it would be easy (...but a mistake) to not check you mirrors for that long.
Wear your safety gear.
Keep your head on a swivel.
Don't take it out on the track if you can't afford to ball it up.
